The fall of Mecca was the signal for an unprecedented rush to accept Islam. As 'Amr ibn Salamah, a foster son and companion of the Prophet, stated:
"The Arabs were waiting for the Quraish to accept Islam. They used to say that Muhammad (s.a.w.a.) must be left to his people. If he would emerge victorious over them, he is undoubtedly a true prophet. When Mecca was conquered, all the tribes hastened to accept Islam."
Zakah collectors were sent into the territories that came under the Muslims' control. These officials not only demonstrated great fairness in collecting the zakah and jizyah, but also preached effectively to the people, for most of them were pious and God-fearing people. After the fall of Mecca, teachers were sent in all directions to bring the people to God's way, and they met with so much success that hosts upon hosts flocked to the Prophet. It is about such mass conversions that the Qur'an has stated:
When there comes assistance from Allah and victory, and you see men entering the religion of Allah in companies. (Qur'an, 110:1-2).
After the order was issued prohibiting the polytheists from entering the Sacred Mosque, the entire Hijaz was Muslim.
By the 10th of Hijra, the influence of Islam had reached Yemen, Bahrain, Yamama, Oman, Iraq, and Syria. The Chief of the Daws, a tribe in Yemen, had accepted Islam even before the emigration. In 8 A.H., Khalid was sent to Yemen to preach Islam but could not make much headway. Then 'Ali went there and read the epistle of the Prophet; the entire tribe of Harridan accepted Islam. In 10 A.H., Wabr was deputed to contact the leading Persians residing in Yemen. Firoz Dailami, Markabood and Wahb ibn Munabbih accepted Islam through him. Ma'adh ibn Jabal and Abu Musa al-Ash'ari were also sent to Yemen with the following instructions:
"Be polite, not harsh; give glad tidings to the people and condemn them not. Work together. When you meet people who already follow some religion, preach to them about the Oneness of God and (my) Messengership; if they accept, tell them that God has enjoined prayers five times in a day and night. If they agree to do so, tell them that zakah is also obligatory upon those who can afford to pay in order to help the poor. If they give zakah do not pick out only things of better quality. Beware of the curse and the supplication of victims, for they reach straight to God."
Their efforts met with considerable success. Meanwhile, Khalid was inviting people to the faith in Najran and the tribe of Abdul-Madan came forward to accept it.
In 8 A.H., Munqir ibn Habn of the tribe of 'Abdul-Qais of Bahrain visited Medina and accepted Islam. Through his efforts and those of his father, their tribe entered the fold and sent a deputation of fourteen persons to the Prophet. In the same year, 'Ala al-Hadhrami was sent to Bahrain to preach to the people. He succeeded in converting its governor, Mundhir ibn Sawa and the public followed suit.
Similarly, Abu Zaid al-Ansari and 'Amr ibn al-'Aas were sent to Oman in 8 A.H. with letters from the Prophet to its chieftains Ubaid and Jaifar. When the chieftains accepted Islam, the whole tribe of Azd responded favorably to the invitation. [The original letter has now been discovered, and its photo was published in the Light magazine (Dar-es-salaam), of June 1978].
By 9 A.H., Islam was gaining some adherents in Syria. Its governor, Farwah, became Muslim. When the Roman emperor learned about it, Farwah was guillotined. He died with a couplet on his lips saying: "Convey my message to the Muslim leaders that I sacrifice my body and honor in the way of God."
As Islam started spreading to the farthest corners of Arabia, a large number of deputations from different tribes began pouring into Medina. Ibn Ishaq has given details of fifteen of them. Ibn Sa'd describes seventy deputations, and the same number is mentioned by al-Damyati, al Mughaltai and Zainuddin al-Iraqi. Hafiz Ibn Qaiyyim and al-Qastalani have critically verified the accounts of these deputations and have themselves given details of thirty-four others.
It was thus, and thus alone, that Islam gradually spread. During a short period of time, it blazed in radiant splendor over the continents.
An Expedition to Tabuk (Rajab, 9 A.H.)
The indecisive battle at Mu'ta had stirred a considerable chagrin to the Roman emperor, Heraclius. Elated by his victories over the Persians and apprehensive of the growing power of the Muslims, he directed his feudatories to collect a huge force to invade Arabia. The tribes of Lakhm, Hudham, Amela and Ghassan gathered to help the Roman army. When news of this preparation reached Medina through a trade caravan, it caused a great deal of anxiety among the Muslims. How alarmed they were can be judged from one incident: A neighbor of 'Umar knocked at his door in the night. When 'Umar came out and inquired what the matter was, the visitor said a calamity had befallen. 'Umar asked whether the Ghassanids had come. The visitor was perturbed over another matter but the attack of the Ghassanids was considered so imminent that Umar's frst thought went to it. In order to meet this danger, the Prophet hastily collected a force of 30,000 volunteers with 10,000 horses among them. In spite of the severe famine that had overtaken Najd and Hijaz and the intense heat of the weather, his people rallied around him. Those who were in a position to do so generously donated large sums of money to meet the expenses of the expedition and to buy weapons and armor to those who could not afford to buy them. This was the first occasion when an appeal for public donations was made, and many Muslims responded generously.
An old and very poor woman brought a small quantity of dates as her contribution. Some hypocrites ridiculed her, but the Holy Prophet said that her contribution was more precious in the sight of Allah than that of many people who had contributed only to show off.
The Holy Prophet left 'Ali as his deputy in Medina. 'Ali exclaimed with dismay, "Are you leaving me behind?" The Prophet said, "'Ali! Are you not satisfied that you have the same position in relation to me as Aaron had with Moses, except that there is no prophet after me?" The Prophet thereby meant that as Moses had left Aaron behind to look after his people when he went to receive the Commandments, he was likewise leaving 'Ali behind as his deputy to look after the affairs of the Muslims during his absence.
The Prophet marched at the head of this force to Tabuk, a place situated midway between Medina and Damascus. There, they came to know, to their relief, that the news of the Ghassanids' attack was incorrect. Having stayed for twenty-four days at Tabuk, the Muslim army returned to Medina.
The Prophet had marched to Tabuk in order to forestall the Ghassanids and the Byzantines, but a certain Western historian has surmised that the aim of this expedition was expansion, viz. to capture the trade routes leading to the more prosperous towns of Syria. Had this been so, there was no sense in returning to Medina without even attempting to fulfill that object after having taken all the trouble and the expenditure over the expedition during the most inconvenient time of the year. But these detractors have their own mission to fulfill.