Imam Sadiq (A.S.) has stated:
I always spread my father’s bed at nights. Once I was awaiting for him, but he didn’t come. I went to the mosque and looked for him. I saw that he was alone in prostration. I went forward slowly. I heard he was saying to God while crying.
O’ Allah! You are pure and guiltless, and really You are my God. O’ Allah! I prostrate only for You as a worship. O’ God my pray and worship is little, increase it by Your Mercy. O’ God! Protect me from Your torture when You gather Your slaves. And accept my repentance, since You are so Merciful. (Forou Kafi, Vol. 3, p.323)
That holy Imam was praying at the last moment of his life when he was poisoned by the ruling Umayyad caliph.
source : http://abna.ir/