Musnad Ahmad 1060:19

Abu Ja'far al-Mada'ini narrated to us, 'Abbad ibn al-'Awwam informed us, from Sa'id ibn Iyas, from Abu al-Ward, from Abu Muhammad al-Hadrami, from Abu Ayyub al-Ansari, who said: When the Messenger of Allah (peace and blessings of Allah be upon him) arrived in Medina, he stayed with me. He said to me: "O Abu Ayyub, shall I not teach you?" I said: "Yes, O Messenger of Allah." He said: "There is no servant who says when he enters the morning: 'There is no god but Allah alone, He has no partner, to Him belongs the dominion and to Him belongs the praise,' except that Allah writes for him ten good deeds for it, erases from him ten evil deeds, and it is for him with Allah equivalent to the freeing of ten slaves, and he is in a shield from Satan until he enters the evening. And he does not say it when he enters the evening, except that it is the same." I said to Abu Muhammad: "Did you hear it from Abu Ayyub?" He said: "By Allah, I heard it from Abu Ayyub narrating it from the Messenger of Allah (peace and blessings of Allah be upon him)."