Yunus and Mansur narrated from Hasan al-Basri (may Allah have mercy on him) that when a woman testifies about a man and his wife that she has breastfed both of them, Hasan al-Basri (may Allah have mercy on him) once said: "If she is trustworthy." And on another occasion he said: "If she is just, then she should be made to swear by Allah that she has breastfed them; if she takes the oath, then separation should be made between the two of them." Hushaym said: "We do not act upon this."
Hadith Referenceسنن سعید بن منصور / كتاب النكاح / 2171