Musnad Ahmad Hadith 21317

Mutarrif says that once I was sitting with some people of the Quraysh when a man came and started praying. He would perform ruku and sujood, then stand up and again perform ruku and sujood, and would not sit in between. I said, "By Allah! It seems as if he does not know anything, whether to end the prayer with salam on even or odd rak'ahs." The people said to me, "Why don't you go to him and explain to him?" So I went to him and said, "O servant of Allah! It seems you do not know whether to finish the prayer on even or odd rak'ahs." He said, "Allah knows, I heard the Prophet Muhammad (peace be upon him) say: 'Whoever performs a sajdah for Allah, Allah writes for him one good deed, erases one sin, and raises him one degree.'" I asked him, "Who are you?" He replied, "I am Abu Dharr." So I returned to my companions and said, "May Allah give you a bad reward on behalf of your companions; you sent me to teach religion to a companion of the Prophet Muhammad (peace be upon him)."