Ali ibn Rabi'a (R.A.A) said "I saw Ali ibn Abu Talib (R.A.A.) once, when he was about to ride. When he inserted his foot in the stir-up he said: 'Bismillah' (in the name of Allah), and when he leveled himself on the saddle he said: praise be to Allah, 'Praised be to He Who hath subdued these unto us, and we were not capable of subduing them and Lo! Unto our Lord we are returned'. Then he praised Allah three times, and magnified (Him) three times. Then, he said: 'Glory be Thee! There is no God but You, I have wronged my soul, forgive me'. Then he smiled. We asked, 'O Leader of the believers! Why did you smile?' he replied, 'I have seen Allah's Messenger صلى الله عليه وسلم doing like what I have just done and then smiled, so I asked: 'O Messenger of Allah! Why did you smile?' He said ' Allah, the Exalted & the Most-High, expresses His pleasure with a servant who asks: O my Lord! Forgive me. Allah says 'My servant has known that none forgives sins save Me'". [Abu Da'ood, Nisa'i, Hakim, Ahmed, and Tirmidhi, and said Authentic]