Sahih Bukhari
Military Expeditions led by the Prophet (pbuh) (Al-Maghaazi)
Volume: 005 / Book Number: 059 / Hadith Number: 352
Narrated Nafi: Ibn 'Umar used to kill all kinds of snakes until Abu Lubaba Al-Badri told him that the Prophet had forbidden the killing of harmless snakes living in houses and called Jinan. So Ibn 'Umar gave up killing them.