Musnad Ahmad 962:52

Nuh ibn Maymun narrated to us, he said: Abu Abd al-Rahman is Abu Muhammad ibn Nuh, and he is the one who was beaten. Abu Khuraym Uqbah ibn Abi al-Sahba’ narrated to us, Abu Ghalib al-Rasibi narrated to me, that he met Abu Umamah in Homs and asked him about things. He narrated to them that he heard the Prophet, may Allah bless him and grant him peace, saying: "There is no Muslim servant who hears the call to prayer, then stands up for his ablution, except that he is forgiven with the first drop that touches his palm from that water. Then, by the number of those drops, until he finishes his ablution, he is forgiven for his past sins, and he stands for his prayer, and it is a supererogatory act." Abu Ghalib said: I said to Abu Umamah: "Did you hear this from the Prophet, may Allah bless him and grant him peace?" He said: "Yes, by the One who sent him with the truth as a bearer of glad tidings and a warner, not once, nor twice, nor three times, nor four, nor five, nor six, nor seven, nor eight, nor nine, nor ten, and ten," and he clapped his hands together.