Musnad Ahmad 27:1191

Abu Abd al-Rahman narrated to us, Sa'id narrated to us, Yazid ibn al-Had narrated to me, from Nafi', from Ibn Umar, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The fire is an enemy, so beware of it." He said: So Abdullah used to follow the fires of his family and extinguish them before he would go to sleep.