Sahih al-Bukhari, Book 97, Hadith 128 (In-Book) ⓘ
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.'"
حَدَّثَنَا مُسَدَّدٌ، حَدَّثَنَا سُفْيَانُ، عَنْ صَالِحٍ، عَنْ عُبَيْدِ اللَّهِ، عَنْ زَيْدِ بْنِ خَالِدٍ، قَالَ مُطِرَ النَّبِيُّ صلى الله عليه وسلم فَقَالَ " قَالَ اللَّهُ أَصْبَحَ مِنْ عِبَادِي كَافِرٌ بِي وَمُؤْمِنٌ بِي " .
also referenced under: Hadith 7503 (DarusSalam) & Volume 9, Book 93, Hadith 594 (USC-MSA)