Musnad Ahmad 937:163

'Abd al-Razzaq narrated to us, he said: I heard al-Awza'i saying: Harun ibn Ri'ab informed me, from al-Ahnaf ibn Qays, who said: I entered Bayt al-Maqdis (Jerusalem) and found a man in it who was prostrating frequently, and I felt something in myself regarding that. When he finished, I said: "Do you know whether you finished on an even number or an odd number?" He said: "If I do not know, then Allah, the Mighty and Majestic, knows." Then he said: "My beloved, Abu al-Qasim, may Allah bless him and grant him peace, informed me." Then he wept. Then he said: "My beloved, Abu al-Qasim, may Allah bless him and grant him peace, informed me." Then he wept. Then he said: "My beloved, Abu al-Qasim, may Allah bless him and grant him peace, informed me that he said: 'There is no servant who prostrates a prostration to Allah, except that Allah raises him a degree by it, removes a sin from him by it, and writes a good deed for him by it.'" He said: I said: "Inform me, who are you, may Allah have mercy on you?" He said: "I am Abu Dharr, the companion of the Messenger of Allah, may Allah bless him and grant him peace." So I felt small in my own estimation.