Muwatta Malik, Book 30, Hadith 1285 (In-Book)

Yahya related to me from Malik that Yahya ibn Said said that he heard Said ibn al-Musayyab say, "Suckling is only while the child is in the cradle. If not, it does not cause flesh and blood relations."

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ يَحْيَى بْنِ سَعِيدٍ، أَنَّهُ قَالَ سَمِعْتُ سَعِيدَ بْنَ الْمُسَيَّبِ، يَقُولُ لاَ رَضَاعَةَ إِلاَّ مَا كَانَ فِي الْمَهْدِ وَإِلاَّ مَا أَنْبَتَ اللَّحْمَ وَالدَّمَ ‏.‏

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also referenced under: Book 30, Hadith 11 (USC-MSA)