It is narrated from Sayyiduna Anas bin Malik (may Allah be pleased with him) that a man passed by the Prophet (peace and blessings be upon him) while some people were with him (peace and blessings be upon him). One of the men who were there said: "I love this man for the sake of Allah." The Prophet (peace and blessings be upon him) asked: "Have you told him?" He said: "No." He (peace and blessings be upon him) said: "Then get up, go to him and tell him." So he went to him and told him, and he (replied): "'Ahabbaka alladhi ahbabtani lahu' (May the One for whose sake you love me love you)." The narrator said: Then that man returned to the Prophet (peace and blessings be upon him) and asked him, and told him (peace and blessings be upon him) what the (other) man had said. The Prophet (peace and blessings be upon him) said: "You will be with the one you love, and you will have the reward that you hoped for (from Allah)."
No one narrated this hadith from Ash'ath bin Abdullah (may Allah have mercy on him) except Ma'mar (may Allah have mercy on him).
Hadith Referenceالمعجم الأوسط / باب الألف / 2994
Hadith Takhrij«أخرجه ابن حبان فى «صحيحه» برقم: 571، والضياء المقدسي فى «الأحاديث المختارة» برقم: 1547، 1548، 1618، 1619، 1703، والحاكم فى «المستدرك» برقم: 7414، والنسائي فى «السنن الكبرى» برقم: 9939، 9940، 9941، وأبو داود فى «سننه» برقم: 5125، وأحمد فى «مسنده» برقم: 12625، 12709، 12785، 13739، وأبو يعلى فى «مسنده» برقم: 3442، وعبد بن حميد فى «مسنده» برقم: 444، والبزار فى «مسنده» برقم: 6533، وعبد الرزاق فى «مصنفه» برقم: 20319»