Sahih Adab al-Mufrad

It is narrated from Sayyiduna Anas bin Malik, may Allah be pleased with him, who said that the Prophet, peace and blessings be upon him, was the most compassionate of all people towards his family. There was an infant at the outskirts of Madinah, and the husband of his nursing mother was a blacksmith. The Prophet, peace and blessings be upon him, used to visit this child. He would find that the blacksmith had burned izkhar (a type of grass), filling the whole house with smoke. The Prophet, peace and blessings be upon him, would kiss the child and hold him close to his mouth (smelling him).