Volume 9 · Book 93 · Hadith 594
Narrated Zaid bin Khalid: It rained (because of the Prophet's invocation for rain) and the Prophet said, "Allah said, 'Some of My slaves have become disbelievers in Me, and some others, believers in Me.'"
— Sahih Bukhari, Volume 9, Book 93: Oneness, Uniqueness of Allah (Tawheed), Hadith #594