It is narrated from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both), (the narrator said:) to my knowledge he narrated this hadith only as the Prophet's own words (marfu'), that the Prophet (peace and blessings be upon him) used to order the killing of snakes, and he said: "Whoever leaves them out of fear or dread of revenge is not one of us." And Sayyiduna Ibn Abbas (may Allah be pleased with them both) said: "Snakes are a transformed form of the jinn, just as some of the Children of Israel were transformed into apes."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 11796