Fiqh-us-Sunnah Volume 1, Purification and Prayer, Fiqh 1.001B.

Section : Rain water, snow, and hail.

These substances are pure because Allah says so: “And sent down water from the sky upon you, that thereby He might purify you…” (al-Anfal 1), and “We send down purifying water from the sky” (al-Furqan 48). This is also supported by the following hadith: Abu Hurairah reported that the Messenger of Allah, upon whom be peace, used to be silent between the (opening) takbir of the prayer and the verbal Qur’anic recitation. Abu Hurairah asked him, “O Messenger of Allah, may my father and mother be sacrificed for you, why do you remain silent between the takbir and the recital? What do you say (silently during that time)?” He said, “I say, ‘O Allah, make a distance between me and my sins similar to the distance you have made between the East and the West. O Allah, cleanse me of my sins in the manner that a white garment (is cleansed) from dirt. O Allah, wash my sins from me with snow, water, and hail.”‘ This hadith is related by the “group”, except for at-Tirmizhi.