It is narrated from Sayyidah Umm Salamah (may Allah be pleased with her) that the Messenger of Allah (peace and blessings be upon him) often used to say this supplication: "O Turner of hearts, keep my heart firm upon Your religion." I said: O Messenger of Allah, why do you make this supplication so often? He (peace and blessings be upon him) said: "O Umm Salamah, the heart of the son of Adam is between two of the fingers of the Lord of the worlds; if He wills, He keeps it upright, and if He wills, He makes it deviate."
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 20167