‘Umar Ibn Al-Khattaab (ra) encouraged the people to perform marriages with different tribes, so that love would develop amongst the people. Therefore, a slave went to a man from the Quraysh and asked him to marry his sister to him, which the latter refused.
‘Umar went to that man and asked him, “Why did you not marry your sister to him? He is a talented and pious individual. You should seek the opinion of your sister; if she accepts the proposal then you should marry her to him.“
The man from the Quraysh accepted the advice of ‘Umar and went to his sister to ask her opinion. She agreed to the marriage and the married his sister to the slave.
[Al-Murtadaa, by An-Nadawee, p. 106]
The Authentic Base 