"Prohibited to you (For marriage) are:- Your mothers, daughters, sisters; father's sisters, Mother's sisters; brother's daughters, sister's daughters; foster-mothers (Who gave you suck), foster-sisters; your wives' mothers; your step-daughters under your guardianship, born of your wives to whom ye have gone in,- no prohibition if ye have not gone in;- (Those who have been) wives of your sons proceeding from your loins; and two sisters in wedlock at one and the same time, except for what is past; for Allah is Oft-forgiving, Most Merciful;" - Quran 4:23 (read more)

"So the Quraish and the Ansar became angry and said, "He (i.e. the Prophet, ) gives the chief of Najd and does not give us." The Prophet said, "I give them) so as to attract their hearts (to Islam)." - Sahih Bukhari 4:55:558 (read more)

"Due to the differences of both lives the Prophet (Sallallahu Alaihi wa Sallam) is not aware of what is going on in this world. He does not know who is asking help from him, and who is seeking child, wealth, wife, etc. ... On the other hand, if it is said that the Prophet (Sallallahu Alaihi wa Sallam) is alive in his grave, it does not mean that his life is similar to the life of those who are living in this world. So, if one seeks his help asks something from him he commits Shirk (polytheism)." - IslamWeb