Abu Hurairah (May Allah be pleased with him) reported: The Prophet (PBUH) said, "A man set out to visit a brother (in Faith) in another town and Allah sent an angel on his way. When the man met the angel, the latter asked him, "Where do you intend to go?'' He said, "I intend to visit my brother in this town". The angel said, "Have you done any favour to him?'' He said, "No, I have no desire except to visit him because I love him for the sake of Allah, the Exalted, and Glorious.'' Thereupon the angel said, "I am a messenger to you from Allah (to inform you) that Allah loves you as you love him (for His sake)".
[Muslim].