Musnad Ahmad 30:801

Yazid narrated to us, Hammad ibn Salamah informed us, from Thabit al-Bunani, from Abu Rafi’, from Abu Hurairah, from the Prophet, peace and blessings of Allah be upon him, who said: "A man went out to visit a brother of his for the sake of Allah, the Almighty and Majestic, in another village. Allah, the Almighty and Majestic, set an angel in wait for him on his path. When he passed by him, he said: 'Where do you intend to go?' He said: 'I intend to go to so-and-so.' He said: 'Is it for a kinship?' He said: 'No.' He said: 'Is it for a favor he has done for you that you are repaying?' He said: 'No.' He said: 'Then why are you coming to him?' He said: 'I love him for the sake of Allah.' He said: 'Indeed, I am a messenger of Allah to you, [informing you] that He loves you because of your love for him for His sake.'"