Musnad Abu Ya'la al-Mawsili 147:16

Al-Abbas ibn al-Walid al-Narsi narrated to us, Wahib narrated to us, from Ayyub, from Amr ibn Sa'id, from Anas, who said: The Messenger of Allah (may Allah bless him and grant him peace) was the most merciful of people toward children. He had a son who was being nursed in a part of Medina, and his foster father was a blacksmith. He would go to him, and we would be with him, while the house was filled with smoke from what he was smoking (the forge). He would smell him, kiss him, and then return.