Hadith 31-285

وَبِهذَا الإِسناد عَنْ عَلِيِ‏ عَلَيْهِ السَّلامُ قالَ: قالَ النَّبِيُ‏ صَلَّى اللهُ عَلَيْهِ وَآلِهِ: مَن قَتَلَ حَيَّةً، فَقَدْ قَتَلَ كافِرَاً.

According to the same documentation, on the authority of Ali (a.s.), the Prophet (S) said, “Whoever kills a snake, it is as if he has killed an atheist.”