From Sahih Bukhari (Hadith 4579):
Narrated Ibn `Abbas:regarding the Divine Verse: "O you who believe! You are forbidden to inherit women against their will, and you should not treat them with harshness that you may take back part of the (Mahr) dower you have given them." (4.19) (Before this revelation) if a man died, his relatives used to have the right to inherit his wife, and one of them could marry her if he wished, or they would give her in marriage if they wished, or, if they wished, they would not give her in marriage at all, and they would be more entitled to dispose her, than her own relatives. So the above Verse was revealed in this connection
Reference: Bukhari 4579