Al-Matalib al-'Aliyah 510 — Ruku, sujud and the remembrance in them

It is narrated from Sayyidah Aishah (may Allah be pleased with her) that she said: It was my turn with the Messenger of Allah (peace and blessings be upon him). He (peace and blessings be upon him) quietly rose from the bed and went out. I thought that perhaps he (peace and blessings be upon him) had gone to one of his other honoured wives, so, moved by the natural feeling of jealousy, I went out after him (peace and blessings be upon him), and suddenly I saw that he (peace and blessings be upon him) was in prostration, lying still like a garment thrown on the ground. I heard him (peace and blessings be upon him) reciting this supplication: 'Sajada laka sawadi wa khayali, wa amana bika fu'adi, hadhihi yadi wa ma janaytu 'ala nafsi, ya 'Azimu yurja li-kulli 'azim, faghfir al-dhanb al-'azim' (O Allah, my being and my inner self have prostrated before You, and my heart has believed in You; here is my hand before You, and I confess the sin and wrong I have done against myself; O Mighty Lord from whom good is hoped for in every great matter, forgive my great sin). Then the Messenger of Allah (peace and blessings be upon him) raised his blessed head and asked: "What brought you out?" I said: I had formed a suspicion. He (peace and blessings be upon him) said: "Indeed, some suspicion is a sin," as Allah Almighty says: "Indeed, some suspicion is sin" [Surah al-Hujurat: 12], "so seek forgiveness from Allah Almighty. Indeed, Jibril (peace be upon him) came to me and ordered me to say these words which you heard, so you too should recite them in your prostration, for any servant who says these words does not raise his head from prostration until he is forgiven."
Musnad Abi Ya'la: 510. Its chain contains Uthman bin Ata al-Khurasani, a da'if (weak) narrator, and his hearing from his father is not established; however, some parts of the supplication are established in other reliable reports.