ما هي الآية الكريمة التي استدل بها علماء الفقه على طهارة ماء المطر، وما وجه الاستدلال بها؟

Rainwater is pure (tahūr), and the proof of this is Allah Almighty's saying: "And We have sent down from the sky pure water" (Quran 25:48), and His saying: "And He sends down upon you from the sky water to purify you thereby" (Quran 8:11). As for the verse from Surah An-Naml: "Is He [not best] who created the heavens and earth and sent down for you from the sky, rain, by which We caused to grow gardens of delight which you could not [otherwise] have grown their trees? Is there a deity with Allah? Rather, they are a people who deviate [from truth]" (Quran 27:60), it is used to infer that Allah Almighty bestowed His grace upon His servants by sending down rain, and this necessitates that it be pure and suitable for benefit.