She was the Prophet Mohammad’s (SAW) cousin. She was first given in marriage by the Prophet Mohammad (SAW) to his adopted son Hadhrat Zaid bin Harithah (Radhiyallaho anho). When Hadhrat Zaid (Radhiyallaho anho) divorced her, she was married to the Prophet Mohammad (SAW) by command of Allah, as mentioned in Surah Al Ahzab. This took place in 5 A.H., at that time she was 35. She was therefore born 17 years before Nubuwwat. She was always proud of the fact that, the other wives while all the other wives were given in marriage did this for her.
When Hadhrat Zaid (Radhiyallaho anho) divorced her and she had completed her Iddat, the Prophet Mohammad (SAW) sent the proposal to her. She said: “I cannot say anything until I have consulted my Allah.” She performed Wudhu, said two rakaat of Salaat, and prayed to Allah: “O, Allah! Thy Prophet proposes to marry me. If I am fit for the honor, then give me in his marriage.” Allah answered her prayer by revealing the following verse to the Prophet Mohammad (SAW) :
“So when Zaid had performed the necessary formality (of divorce) from her, we gave her unto thee in marriage, so that (henceforth) there may be no sin for believers in respect of the wives of their adopted sons, when the latter have performed the necessary formality (of release) from them. The Commandment of Allah must be fulfilled.” (XXXIII:37)
When she received the good news about this revelation, she prostrated before Allah in thanksgiving. Prophet Mohammad (SAW) arranged a big feast of Walimah for this marriage. A goat was slaughtered and mutton-curry with bread was served to the guests. People came in groups, and were served till all of them were fed.
Hadhrat Zainab (Radhiyallaho anha) had a very large heart for spending in the way of Allah. She earned by working with her hands and spent all “her earnings in charity. It was about her that the Prophet Mohammad (SAW) prophesied:
“My wife with long hands will be the first to meet me after my death.” The wives took this to mean the physical length of arms and began to measure their hands with a stick. The hands of Hadhrat Saudah (Radhiyallaho anha) came out to be the longest by measurement. But when Hadhrat Zainab (Radhiyallaho anha) died first, the meaning of the metaphor used by the Prophet Mohammad (SAW) dawned upon them. She fasted very often. She died in 20 and ‘Umar (Radhiyallaho anho) led the funeral service. She fifty at the time of her death.
Source : eislam