Abu Dawud Book 3, Hadith Number 1665.

Narated By Buhaysah al-Fazariyyah : My father sought permission from the Prophet (PBUH). (When permission was granted and he came near him) he lifted his shirt, and began to kiss him and embrace him (out of love for him). He asked: Apostle of Allah, what is the thing which it is unlawful to refuse? He replied: Water. He again asked: Prophet of Allah, what is the thing which it is unlawful to refuse? He replied: Salt. He again asked: Prophet of Allah, what is the thing which it is unlawful to refuse? He said: To do good is better for you.