سنن أبي داود

Bahz b. Hakim on his father's authority said that his grandfather said: I said: Messenger of Allah! to whom should I show kindness? He replied: Your mother, next your mother, next your mother, and then comes your father, and then your relatives in order of relationship. The Messenger of Allah (ﷺ) said: If a man asks his slave whom he freed for giving him property which is surplus with him and he refuses to give it to him, the surplus property which he refused to give will be called on the Day of resurrection as a large bald snake.

Abu Dawud said: Aqra' means a snake whose hair of the head were removed on account of poison.