Mu'awiyah (May Allah be pleased with him) reported:
The Messenger of Allah said, "When Allah wishes good for someone, He bestows upon him the understanding of Deen."[Al-Bukhari and Muslim]. (RU)
App reference (RU): Book 13, Hadith 1 (RU)
Arabic/English book reference (RU): Book 13, Hadith 1376 (RU)