Musnad Ahmed: Hadith 1664

The Messenger of Allah (ﷺ) came out of the mosque and went towards where the zakah was kept. He went in and turned to face the qiblah, then he fell down in prostration and remained in prostration for a long time, until I thought that Allah, may He be glorified and exalted, had taken his soul. I drew close to him and sat down, and he raised his head and said: "Who is this?" I said: "Abdur Rahman. He said: “What do you want?" I said: O Messenger of Allah, you prostrated for so long that I thought Allah, may He be glorified and exalted, had taken your soul. He said: “Jibreel came to me and gave me glad tidings. Allah, may He be glorified and exalted, says: Whoever sends blessings upon you, I shall send blessings upon him, and whoever sends salams upon you, I shall send salams upon him. So I prostrated to Allah, may He be glorified and exalted, out of gratitude."