Sahih Muslim
The Book Pertaining to the Excellent Qualities of the Holy Prophet (may Peace be upon them) and His Companions (Kitab Al-Fadail)
Book Number: 030 / Hadith Number: 5754
'A'isha reported: Never did Allah's Messenger (may peace be upon him) make a choice between two things but adopting the easier one as compared to the difficult one, but his choice for the easier one was only in case it did not involve any sin, but if it involved sin he was the one who was the farthest from it amongst the people.