Musnad Ahmad 32:162

Isma'il narrated to us, Ayyub informed us, from 'Amr ibn Sa'id, from Anas ibn Malik, who said: I have never seen anyone more merciful to children than the Messenger of Allah, may Allah bless him and grant him peace. Ibrahim was being nursed in the high grounds of Medina. He [the Prophet] would set out, and we would be with him, and he would enter the house while it was filled with smoke, for his foster father was a blacksmith. He would take him, kiss him, and then return. 'Amr said: When Ibrahim died, the Messenger of Allah, may Allah bless him and grant him peace, said: "Indeed, Ibrahim is my son, and he died while at the breast, and he has two wet nurses who will complete his nursing in Paradise."