I heard the Messenger of Allah ﷺ say, "There is no heart that is not between two of the fingers of the Most Merciful. If He wills, He keeps it upright, and if He wills, He causes it to deviate."The Messenger of Allah ﷺ used to say, "Steadfaster of hearts, make our hearts steadfast upon Your religion."
سمعت رسول الله ﷺ يقول: ما من قلب إلا بين إصبعين من أصابع الرحمن إن شاء أقامه، وإن شاء أزاغه وكان رسول الله ﷺ يقول: يا مثبت القلوب ثبت قلوبنا على دينك.
Ibn Majah (199) and Ahmad (17630) narrated it, and Ibn Khuzayma graded it sahih in Tawhid (132), as did Ibn Hibban (943) and Hakim (1/525), all of them through the route of Abdul-Rahman bin Yazid bin Jabir, who said, "I heard Busr bin Ubaydullah say, 'I heard Abu Idris Khawlani say, "Nawas bin Saman Kilabi narrated to me,"'" and he mentioned it. The discussion of it is set out at length in the Book of Faith.