Although being much older than Muhammad (S)...
Although being much older than Muhammad (S), (she was 40 years old), the marriage was agreed upon by both families and Muhammad’s uncle Abu Talib read the Khutba of marriage and performed the marriage ceremony according to the Abrahamic traditions. The words of the Khutba as described in Sirat-e-Rasullallah by Ibne Hisham were: “Praises are for Allah who was the God of Ibrahim who worshipped one God and a Muslim. I am the descendent of Ibrahim and have remained on the same religion of One God.
May Allah keep this purity among the descendants of Ibrahim forever”. After this Khutba Abu Talib completed the marriage ceremony between Muhammad (S) and Khadija. Muhammad (S) moved to her house and the partnership from trading to partnership in life began in earnest. A baby daughter was born to Khadija within a few years after the marriage. She was named Fatima (sa). Khadija had two daughters from her earlier marriage which ended in widowhood.
So the three daughters, two from Khadija’s earlier marriages and one from Muhammad (S) grew up together in the same house. History mentions another boy growing up in Muhammad’s house. He was ‘Ali (as) , Abu Talib’s son. ‘Ali (as) was born in the year 30 Amulfeel when Muhammad was 30 years old. Fatima’s birth was recorded some five years later. So the difference of ages between Fatima and ‘Ali was about 5 years.
‘Ali was treated by Muhammad (S) like a son and Muhammad (S) took him everywhere he went. Ibne Hisham in his Sirat mentions that Muhammad (S) began to meditate more and more. He would leave the town of Makka to the nearby hill called Jabal el Noor. There was a cave at the top of the hill and Muhammad (S) would climb the mountain and sit in the cave to meditate. Sometimes he would stay there for days. Many times ‘Ali accompanied him.
One such story tells us that on one occasion Muhammad (S) did not return for 3 or 4 days and Abu Talib was concerned. His son ‘Ali was also with him. They had taken some food with them. So the searching party from Makka went to the mountain looking for the two. When they reached the top and entered the cave they found Muhammad (S) and ‘Ali (as) meditating together, safe and sound. Abu Talib asked Muhammad what he did there.
Muhammad told his uncle that he and ‘Ali were engaged in meditating about the creator of the universe, the God of Ibrahim and Ismael This meditation continued until one day a voice was heard inside the cave. It said, “Read”. Muhammad (S) replied what shall I read.