Musnad Ahmad 937:60

Abu Mu'awiyah narrated to us, Dawud ibn Abi Hind narrated to us, from Abu Harb ibn Abi al-Aswad, from Abu al-Aswad, from Abu Dharr, who said: He was watering [animals] at a cistern of his, and some people came. He said: "Which of you will bring [his animals] to the cistern of Abu Dharr and seek the reward for a few hairs of his head [i.e., perform a small act of patience]?" A man said: "I will." The man came and brought his animals to the cistern, and he broke it [the cistern]. Abu Dharr was standing, so he sat down, then he lay down. It was said to him: "O Abu Dharr, why did you sit, then lie down?" He said: "The Messenger of Allah (peace and blessings of Allah be upon him) said to us: 'If one of you becomes angry while he is standing, let him sit down; if the anger goes away from him, [then that is well], otherwise let him lie down.'"