Sahih Muslim
The Book on Salutations and Greetings (Kitab As-Salam)
Book Number: 026 / Hadith Number: 5546
Nafi' reported that Abu Lubaba talked to Ibn 'Umar to open a door in his house which would bring them nearer to the mosque and they found a fresh slough of the snake, whereupon 'Abdullah said: Find it out and kill it. Abu Lubaba said: Don't kill them, for Allah's Messenger (may peace be upon him) forbade the killing of the snakes found in houses.