Musannaf Ibn Abi Shaybah

Hazrat Aisha (may Allah be pleased with her) narrates that the Messenger of Allah (peace and blessings be upon him) used to supplicate: O Turner of hearts! Make my heart steadfast upon Your religion. I asked: O Messenger of Allah (peace be upon him)! Do you make this supplication? The Prophet (peace be upon him) replied: O Aisha (may Allah be pleased with her)! Do you not know that the heart of the son of Adam is between two fingers of Allah? When He wills, He turns his heart towards guidance, and when He wills, He turns his heart towards misguidance and deviation.