Al-Adab Al-Mufrad #644

Malik ibn Aws ibn al-Hadathan said, "The Prophet, may Allah bless him and grant him peace, went out to open ground to answer a call of nature and did not find anyone to follow him. 'Umar went out and followed him with a clay pot or wudu' vessel. He found him prostrating in a river bed. He fell back and sat behind him until the Prophet, may Allah bless him and grant him peace, lifted his head. He said, 'You have done well, 'Umar. When you found me prostrating, you went behind me. Jibril came to me and said, 'If someone says the prayer on you once, Allah will pray ten times on him and raise him ten degrees.'"