Why would the Messenger of Allah, may Allah bless him and grant him peace, ask Allah for steadfastness in religion by saying: "O Turner of hearts, make my heart steadfast upon Your religion," when it is impossible for him to stray? And how do we ask Allah for steadfastness upon the fitra, when it is already inherent within us?

The Prophet's -peace and blessings be upon him- supplication for steadfastness, just like his request for guidance, is an act of worship to Allah and a teaching for his Ummah. The Ummah, naturally inclined towards Tawhid (monotheism), needs steadfastness because devils strive to mislead it, as stated in the Hadith Qudsi: "I created My servants upright, but the devils led them astray." The Prophet -peace and blessings be upon him- frequently used to say: "O Transformer of hearts, make my heart firm upon Your religion." This does not signify fear for one's faith, but rather because hearts are between two of Allah's fingers, which He turns as He wills. The believer asks for guidance and steadfastness at all times due to their constant need for Allah, as Allah the Almighty said: {O you who have believed, believe in Allah and His Messenger}, meaning, persevere in faith. And as Allah the Almighty said: {Our Lord, do not let our hearts deviate after You have guided us}. So, asking for guidance and steadfastness is not seeking something already attained, but rather a plea for continuity and divine enabling.