Sahih al-Bukhari 2660
Narrated `Uqba bin Al-Harith:
I married a woman and later on a woman came and said, "I suckled you both." So, I went to the 
Prophet (to ask him about it). He said, "How can you (keep her as a wife) when it has been said (that 
you were foster brother and sister)? Leave (divorce) her.
حَدَّثَنَا أَبُو عَاصِمٍ، عَنْ عُمَرَ بْنِ سَعِيدٍ، عَنِ ابْنِ أَبِي مُلَيْكَةَ، عَنْ عُقْبَةَ بْنِ الْحَارِثِ، قَالَ تَزَوَّجْتُ امْرَأَةً فَجَاءَتِ امْرَأَةٌ فَقَالَتْ إِنِّي قَدْ أَرْضَعْتُكُمَا‏.‏ فَأَتَيْتُ النَّبِيَّ صلى الله عليه وسلم فَقَالَ ‏
"‏ وَكَيْفَ وَقَدْ قِيلَ دَعْهَا عَنْكَ ‏"‏ أَوْ نَحْوَهُ‏.‏