Fiqh-us-Sunnah Volume 4, Funerals and Dhikr, Fiqh 4.140A.

Section : Leaving One’s House for What is Dear to Allah.

Abu Hurairah reported that the Prophet, peace be upon him, said, “No one leaves his home without two banners waiting at his door, one of them in the hands of an angel and the other in the hands of a devil. If he intends to do what pleases Allah the angel will follow him with his standard, and he will remain under the banner of the angel until he returns to his house, but if he sets out for what displeases Allah the devil with his banner will follow him about, and he will remain under the devil’s banner until he returns to his house.” (Ahmad and At-Tabarani. Its chain of authorities is sound)