Al-Aswad (may Allah have mercy on him) narrated: Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) recited Surah "Wal-Mursalati 'urfa" and said: This surah was revealed to the Messenger of Allah (peace and blessings be upon him) on Laylat al-Hayyah (the Night of the Snake). We said: O Abu Abd al-Rahman, what is Laylat al-Hayyah? He said: I was with the Prophet (peace and blessings be upon him) that night when a snake came out at us. The Messenger of Allah (peace and blessings be upon him) said: "Search for it." We searched for it, but it eluded us until it went into its hole. Then the Messenger of Allah (peace and blessings be upon him) said: "Leave it; Allah has protected it from your harm, and protected you from its harm."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 10119