Muhammad (S) grew up in his loving uncle's house, blossoming into a handsome youth of exceptionally good character, which marked him out from rest of the young Makkans. He soon began to assist Abu Talib in trade and commerce and once accompanied his uncle's trading caravan to Syria, ably revealing his talents and integrity. His honesty and reputation preceded him and sometime after his return to Makkah he took up a trading job with one of the wealthiest and noblest Quraishite women, Khadija bint Khuwailid. He accepted to work for Khadija and was entrusted with some money, with which he busied himself in commerce. He again travelled to Syria and made great profits for Khadija during the trip.
Naturally Khadija was pleased and soon came to admire Muhammad's (S) intelligence and honesty. Eventually she offered her hand in marriage which was accepted by him. Muhammad (S) thus married Khadija and they lived a harmonious life full of love, co-operation and sincerity, sharing each other's joys and sorrows. They formed a perfect husband and wife pair, the likeness of which is something rare in human history.
When finally the Divine Message was revealed to Muhammad (S), the devout Khadija at once believed in her husband without ever expressing the slightest doubt. She was the first among women to accept Islam and subsequently put all her vast wealth and property at the Prophet's disposal for the spread of truth and justice.
Khadija bint Khuwailid was from the Quraish tribe and was born and bred in Makkah. Even in the days of Jahiliyyah she was known among the Quraish women for her nobleness of character and virtue, that is why she was called by the Makkans as Tahera 'the pure'. She married Muhammad (S), 15 years before revelation came to him from Allah.
As long as she was alive the Prophet never took a second wife and even in later years of his life after numerous marriages, he used to cherish her loving memory and refer to her as the most beloved of his spouses. She endured with him hunger, poverty and calamities inflicted by the Makkan polytheists. She bore Muhammad (S) many children, all of whom except for Fatima (a) died in infancy, including son Qasim1 from whom the Prophet's kunya (agnomen) 'Abul Qasim' is derived.
Finally in the tenth year of the Prophetic mission, shortly after the small Muslim community quarantined by the heathens in Shaib Abi Talib had come out of the valley, Khadija breathed her last. It was a great tragedy for the Prophet. The year is known as the 'Year of Grief' in history because the Prophet suffered a further blow that year losing that other great benefactor, his uncle Abu Talib.