عن أَنسٍ رضيَ اللهُ عنه، أَنَّ رَجُلاً كَانَ عِنْدَ النَّبِيِّ صَلّى اللهُ عَلَيْهِ وسَلَّم، فَمَرَّ رجلٌ بِهِ، فَقال: يا رسولَ اللهِ إِنِّي لأُحِبُّ هَذا، فقالَ لهُ النبيُّ صَلّى اللهُ عَلَيْهِ وسَلَّم: «أَأَعْلَمْتَهُ؟» قَالَ: لا قَالَ: «أَعْلِمْهُ» فَلَحِقَهُ، فَقَالَ: إِنِّي أُحِبُّكَ في اللهِ، فقالَ: أَحَبَّكَ الَّذِي أَحْبَبْتَنِي لَهُ. رواه أبو داود بإِسنادٍ صحيح.

Anas (may Allah be pleased with him) reported that a man was with the Prophet (peace and blessings be upon him) when another man passed by him, and he said: O Messenger of Allah, I truly love this man. The Prophet (peace and blessings be upon him) said to him: "Have you informed him?" He said: No. He said: "Inform him." So he caught up with him and said: I love you for the sake of Allah. The man replied: May He for whose sake you have loved me love you. Reported by Abu Dawud with an authentic chain of narration.