http://theislampath.com/smf/Smileys/default/salam.gif
Salaam/peace
it came later when Zaid had problem with wife & wanted to divorce her .
When thou saidst to him whom God had blessed and thou hadst favoured, ‘Keep thy wife to thyself, and fear God,’ and thou wast CONCEALING WITHIN THYSELF what God should reveal…
he had concealed feelings when she was still a married woman, which is called adultry in the Bible and breaks one of the 10 commandmants.
As to the why it happened after Zaid married her, Al-Tabari states:
Zaynab had dressed in haste when she was told “the Messenger of God is at the door.” She jumped up in haste and excited the admiration of the Messenger of God, so that he turned away murmuring something that could scarcely be understood. However, he did say overtly: "
Glory be to God the Almighty! Glory be to God, who causes the hearts to turn!".
Let’s check what Al-Qurtubi says in this regard (translation from the Arabic link):
quran.al-islam.com/Tafseer/DispTafsser.asp?
l=arb&taf=KORTOBY&nType=1&nSora=33&nAya=50
As for what was granted and made lawful (by Allah) to the prophet –pbuh– they are 16 issues:-
First: To be fair with the spoils.
Second: To (forcefully) take a fifth of a fifth or just a fifth (of the spoils of war).
Third: “Al Wisal” (Dimitrius- the fast or fasting. This usually refers to fasting or abstaining from food.)
Fourth: To take more than four women.
Fifth: To marry, “Yas-tan-kih” (or have intercourse), with a woman who verbally pronounces her dedication (to the prophet).
Sixth: To marry, “Yas-tan-kih,” without the presence (or permission) of a legal guardian.
Seventh: To marry, “Yas-tan-kih,” without a dowry.
Eighth: To marry (and have intercourse) during a state of ritual consecration and purification.
Ninth: The annulment of an oath he may make to his wives.
Tenth:** If Muhammad looks at a woman (and desires her) THEN IT IS NECESSARY FOR HER HUSBAND TO DIVORCE HER AND FOR MUHAMMAD TO MARRY HER**. Ibn Al A’raby said, “This is what the servant of the two holy mosques has also said, as was clear to the scholars **FROM THE STORY OF ZAID **which also had this meaning.”
Eleventh: That the prophet released Safiyyah (from her captured status) and he considered her release as her dowry.
Twelfth: To enter Mecca without being in a state of ritual purification.
Thirteenth: To fight in Mecca.
Fourteenth: That he is not inherited by anyone at all. This was mentioned in the oath of absolution for when a man approaches death due to illness, most of his possessions are taken away, so that he does not have more than a third left for him. But the possessions of the prophet remained for him, as is evidenced in the verse of inheritance and in Surat Mariam.
Fifteenth: His marriage is still considered effective after his death.
Sixteenth: If he divorces a woman she remains prohibited to everyone and may not be married, “Nikah,” to someone else.
Al-Sira al-Halabiyya, agrees with al-Qurtubi that Muhammad could have caused a man to divorce his wife if he so desired to have her:
“If Muhammad lusted after a married woman, it became a must for her husband to divorce her for him.” (Al-Halabi, Al-Sira al-Halabiyya, Volume III, p. 377)
Al-Zamakhshari’s commentary on this subject:
Keep thy wife to thyself: that is, Zainab bint Jahsh. After having given her to Zaid ibn Haritha as a wife, the Messenger of God once caught sight of her,
and she made an impression of him. At this sight he said: ‘**Praise be to God who changes the heart!’ **Previously his soul had turned away from her so that he had not desired her (as a wife). If he had desired her at that time, he would have asked her for her hand in marriage. Now Zainab heard of this praise and mentioned it to (her husband) Zaid, who understood and to whom God gave antipathy against her and aversion to intimacy with her. So Zaid said to the Messenger of God: ‘I might divorce my wife’; to which the latter replied: ‘What is it? Has something filled you with mistrust against her?’ Zaid answered: ‘By God, no! I have observed only good in her; yet her noble rank places her too high above me and causes me to feel hurt.’ Thereupon the Messenger of God said: ‘Keep thy wife to thyself and fear God.’ But Zaid (nevertheless) separated from her, and as soon as the waiting period (during which the wife may enter into no new marriage) had elapsed, the Messenger of God had said (to Zaid): ‘I have no one whom I trust more than you; therefore, seek the hand of Zainab for me!’