Al-Adab Al-Mufrad, Hadith 375 ⓘ
Jarir reported that the Prophet, may Allah bless him and grant him peace, said, "Allah will not show mercy to a person who does not show mercy to other people."
حَدَّثَنَا مُسَدَّدٌ، قَالَ: حَدَّثَنَا يَحْيَى، عَنْ إِسْمَاعِيلَ قَالَ: أَخْبَرَنِي قَيْسٌ قَالَ: أَخْبَرَنِي جَرِيرٌ، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ: مَنْ لا يَرْحَمُ النَّاسَ لا يَرْحَمُهُ اللَّهُ.
also referenced under: Book 20, Hadith 4 (In-Book) & Book 20, Hadith 375 (English)