Musnad Ahmad 1153:1160

Muhammad ibn Bakr narrated to us, Ibn Jurayj informed us, Ibn Abi Mulaykah informed me, from Aisha, who said: I missed the Prophet, may Allah bless him and grant him peace, one night, and I thought he had gone to some of his wives. Abd al-Razzaq said: So I searched for him, then I returned, and behold, he was bowing or prostrating, saying: "Glory be to You and with Your praise, there is no god but You." I said: "May my father and mother be sacrificed for you, you are indeed in a state [of worship], and I am in another."