The advancement of Islam and its penetration into different peoples took place gradually. In the terminology of the Holy Qur'an those persons who preceded all others in embracing and propagating Islam are called as-Sabiqun (the preceding ones), and in the early days of Islam this precedence was in itself a criterion of virtue and superiority and, even amongst these persons, one who preceded another one enjoyed a more honourable position. Hence, we should consult the authentic sources and decide, without any bias, as to who were the first amongst men and women who embraced Islam.
THE FIRST AMONGST WOMEN
It is an admitted historical fact that from amongst women Khadijah was the first to embrace Islam and there is no contradictory report on this point. We briefly mention here an important historical authority which has been quoted by the historians from one of the wives of the Holy Prophet.
A'isha says: "I was always sorry for not having seen the period of Khadijah and wondered at the kindness and love which the Holy Prophet expressed for her, because her dear husband always remembered her more than anyone else and if he slaughtered a sheep he found out the friends of Khadijah and sent them a share of the meat. One day, when the Holy Prophet was going out of the house, he remembered Khadijah and praised her. Eventually I could not control myself and said very boldly: "She was nothing more than an old woman and Allah has given you a better one".
My words had a very unfavourable effect on the Holy Prophet of Allah. Signs of anger and wrath appeared on his forehead and he said: "It is not at all so... I have not acquired a better one. She believed in my Prophethood when all people were drowned in infidelity and polytheism. She placed her wealth at my disposal in the most trying circumstances. Allah gave me through her issues, which I did not get through anyone else.
Another evidence about Khadijah being the first woman in the world to embrace Islam is the very incident of the commencement of the revelation of the Holy Qur'an, because, when the Holy Prophet came down from the cave of Hira and related the incident to his wife she immediately confirmed her husband's statement and consoled him. Furthermore, she had time and again heard from the fortune-tellers and sages of Arabia about the prophethood of her husband and it was on account of the truthfulness and righteousness of the Hashmite young man that she married him.
THE FIRST AMONGST MEN
Almost all the Shi'ah and Sunni historians are unanimous that the first amongst men to embrace Islam was Ali. As against this well-known statement there can also be found some rare statements, in history. Their narrators have chosen to state the reverse of it. For example, it is said that the first man to embrace Islam was either Zayd bin Harith or Abu Bakr. However, most of the arguments bear evidence against these two statements. Some of these are as follows:
THE FIRST EVIDENCE
Ali had been brought up from his very childhood in the house of the Holy Prophet and the latter endeavoured to educate him like a kind father. Most of the biographers say unanimously: "Before the appointment of Muhammad to the prophetic mission a severe drought appeared in Makkah. Abu Talib, the uncle of the Holy Prophet, had a big family to support. He was the chief of Quraysh, and his income was not at all in keeping with his expenditure and he was not as wealthy as his brother Abbas. The financial condition of Abu Talib prompted the Holy Prophet to discuss the matter with his uncle Abbas and they decided to take some of the children of Abu Talib to their own houses so as to alleviate his burden and to help him meet his requirements. Consequently the Prophet took Ali to his house and Abbas took Ja'far under his guardianship".
In the circumstances it can be said that, when Ali went to the Holy Prophet's house his age was not less than eight or ten years. The reason for this presumption is that the object of the Holy Prophet in taking Ali under his patronage was to alleviate the burden of the chief of Makkah (Abu Talib) and besides the fact that separation of a child from his parents who is less than eight or ten years, is a difficult matter; it could not also have any appreciable effect on the conditions of life of Abu Talib.
Hence, it is necessary that we should presume the age of Ali at that time to be such that his being taken away from Abu Talib had an appreciable effect on the latter's conditions of life. In the circumstances how can it be said that strangers like Zayd bin Harith and others had become acquainted with the secrets of revelation, whereas the cousin of the Holy Prophet, who was nearest to him of all others and was always with him, remained ignorant of them?
The purpose of the Prophet in fostering Ali was to compensate Abu Talib to some extent for the services rendered by him and so far as the Prophet was concerned there was nothing more dear to him than to guide a person directly. Keeping all these things in view how can it be said that the Holy Prophet kept his cousin deprived of this great blessing, notwithstanding the fact that he (Ali) was an intelligent person with a highly enlightened mind? It would be better if we learn about this matter from the lips of Ali himself: In the sermon entitled Qasi'ah he explains his rank and esteem in the eyes of the Prophet thus: "You know the esteem in which the Holy Prophet held me on account of our near relationship and the high position and respect (which I enjoyed in his eyes). During my childhood he fostered me under his own care and stuck me to his bosom. He embraced me in his bed and I used to smell his sweet smell. I followed him just as the off-spring of a she-camel follows its mother. Every day he hoisted (showed) a sign of his moral virtues and ordered me to follow it. He stayed in Hira every year (before his appointment to the prophetic mission) and I used to go and see him there, whereas none else saw him.
At that time Islam had not reached any house except that of the Holy Prophet and Khadijah, and I was the third amongst them. I used to see the light of revelation and messengership and smelt the fragrance of prophethood".
THE SECOND EVIDENCE
Narrating the life history of Afif Kandi, Ibne Hajar (in 'Al-lsabah), Ibne Abdul Bir (in Isti'ab) and many other scholars of history have quoted him to have said: "During the Age of Ignorance I once went to Makkah. My host was Abbas son of Abdul Muttalib and both of us arrived in the precincts of the Holy Ka'bah. Suddenly l saw that a man came and stood by the side of the Ka'bah. Then a boy arrived and stood on his right side. Soon after that I saw a woman came and stood behind them. I saw the boy and the woman performing ruku' and sujud (kneeling and prostration) in imitation of the man. This unprecedented scene inspired me to enquire from Abbas about it. He said: "That man is Muhammad son of Abdullah and that boy is his cousin and the woman standing behind them is the wife of Muhammad". Then he added: "My nephew says that a day will come when he will control the treasuries of 'Kisra' and 'Kaiser'. By Allah, there is no follower of this religion on the face of the earth except these three". Then the narrator says: "I wish that I had been the fourth of them!"
Since the above narrative is not directly concerned with Ali, even those persons, who fail to narrate his virtues have quoted it. Amongst the traditionalists only Bukhari has thought it proper to declare it 'weak', but his attitude towards the progeny of the Holy Prophet's household is quite well-known. The readers can study the said narrative in detail in the books mentioned below.
THE THIRD EVIDENCE
In the sermons and dissertations of Ali we usually come across the following and other similar sentences:
"I am the servant of Allah and the brother of the Holy Prophet and the greatest truthful one, and none will utter this sentence after me except one who is a liar. I offered prayers along with the Holy Prophet for seven years before anyone else did so."
The author of al-Ghadir (vol. III, page 222) has quoted authorities for these narrations from the books of traditions and history and we dispense with quoting the same briefly:
THE FOURTH EVIDENCE
The following traditions of the Holy Prophet narrated by successive witnesses with various explanations have been quoted to this effect:
"The first person who will meet me on the Pool of 'Kauthar' and the first person who embraced Islam is Ali son of Abu Talib".
You may also study the authorities for these traditions in the third volume of 'al-Ghadir', page 320. The evidences for both the parts have reached the stage of consecutiveness and when a person studies these ahadith without any bias he becomes definite about Ali being the foremost among the believers. He does not, therefore, prefer at all the other two statements which are in a minority from the point of view of narration. The number of the supporters of the first statement (viz. Ali was the first person to embrace Islam), who consist of distinguished companions of the Prophet and tabe'in (companions of the companions of the Prophet) exceeds sixty. So much so that even Tabari  who has left the matter open and has contented himself only with quoting the statement says that Ibn Sa'id asked his father: "Was Abu Bakr the first person to embrace Islam? " His father replied: "No. Before he embraced Islam more than fifty persons had come round to the Prophet's way. However, his Islam was superior to the Islam of others."
MAMUN'S DISCUSSION WITH ISHAQ
Ibn Abd Rabbih quotes an interesting incident in 'Aqdul Farid' which may be summarized as under:
Mamun arranged a debating assembly and the famous scholar Ishaq occupied the foremost position in it. When Ali's precedence over others in the matter of acceptance of Islam was established, Ishaq said "When Ali embraced Islam he was only a boy but Abu Bakr was a mature man (at the time he became a Muslim). Hence his faith enjoys superiority over that of Ali".
Mamun suddenly intervened and said: "Did the Prophet invite Ali in his boyhood to adopt the faith, or his faith was due to divine inspiration? It cannot at all be said that his faith was inspired, because, not to speak of Ali, even the faith of the Prophet was not inspired but was the result of guidance and messages brought by Jibreel from Allah. Hence, when the Holy Prophet invited him to accept Islam, did he do so on his own account or had he been ordered by Allah to accomplish the deed? We cannot imagine that the Prophet should subject himself or anyone else to hardship and responsibility without an order from Allah. Hence there is no alternative except that we should say that the Prophet's call is supported by divine order. And does the Omniscient Lord order His Prophet to invite an untalented boy (for whom 'faith' or 'no faith' are alike) to adopt Islam? Certainly such an act is not possible from the All-Wise and All-Knowing Allah.
Hence, it should be concluded that the faith of Ali was a true and firm faith which was not at all inferior to the faith of others and it is Ali, son of Abu Talib to whom the verses of Qur'an "and the foremost are the foremost, these are they who are drawn nigh (to Allah)", most appropriately applies.
 Biharul Anwar, vol. XVI, page 8.
 Seerah Ibn Hisham, vol. I, page 246.
 Nahjul Balaghah, vol. II, page 182.
 Tarikh-i Tabari, vol. II. p. 211; Tarikh-i Kamil, vol. II, pp. 31 - 38, and A'lamul Wara, page 25.
 In some of the narratives the period has been mentioned to be five years and on the basis of numerous indications it may be said that a part of this period preceded to the prophetic mission.
 2Tarikh-i Tabari, vol. II, page 215. .