Sunan Abi Dawud, Hadith 5106 ⓘ
Narrated Anas ibn Malik: A man was with the Prophet and a man passed by him and said: Messenger of Allah! I love this man. The Messenger of Allah then asked: Have you informed him? He replied: No. He said: Inform him. He then went to him and said: I love you for Allah's sake. He replied: May He for Whose sake you love me love you!
حَدَّثَنَا مُسْلِمُ بْنُ إِبْرَاهِيمَ، حَدَّثَنَا الْمُبَارَكُ بْنُ فَضَالَةَ، حَدَّثَنَا ثَابِتٌ الْبُنَانِيُّ، عَنْ أَنَسِ بْنِ مَالِكٍ، أَنَّ رَجُلاً، كَانَ عِنْدَ النَّبِيِّ صلى الله عليه وسلم فَمَرَّ بِهِ رَجُلٌ فَقَالَ يَا رَسُولَ اللَّهِ إِنِّي لأُحِبُّ هَذَا . فَقَالَ لَهُ النَّبِيُّ صلى الله عليه وسلم " أَعْلَمْتَهُ " . قَالَ لاَ قَالَ " أَعْلِمْهُ " . قَالَ فَلَحِقَهُ فَقَالَ إِنِّي أُحِبُّكَ فِي اللَّهِ . فَقَالَ أَحَبَّكَ الَّذِي أَحْبَبْتَنِي لَهُ .
also referenced under: Hadith 5125 (DarusSalam)