Mishkat al-Masabih 13 Marriage كتاب النكاح 91

وَعَنْ أُمِّ سَلَمَةَ قَالَتْ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «لَا يُحَرِّمُ مِنَ الرِّضَاعِ إِلَّا مَا فَتَقَ الْأَمْعَاءَ فِي الثَّدْيِ وَكَانَ قبل الْفِطَام» . رَوَاهُ التِّرْمِذِيّ

Umm Salama reported God’s Messenger as saying, “The only suckling which makes marriage unlawful is that which is taken from, the breast and enters the bowels, and is taken before the time of weaning.” Tirmidhi transmitted it.