Sayyiduna Abu Ayyub al-Ansari (may Allah be pleased with him) says: I heard the Messenger of Allah (peace and blessings be upon him) say: "Whoever separates a mother and her child, Allah will separate him from his loved ones on the Day of Resurrection."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 18309