Hadrat Abdullah ibn Amr bin Al-Aas (r.a.) reported: ‘The Messenger of Allah (peace be upon him) would supplicate: "Allahumma musarrifal-qulubi, sarrif qulubana 'ala ta'atika. (O Allah! Controller of the hearts, direct our hearts to Your obedience)."’
Related by Muslim. Hadith quoted from Riyad-us-Saliheen (Hadith # 1470)
One’s heart is always open to trouble, turmoil, and ordeals as one drifts from one situation or trial to another. If one is not supported by Allah Subhanah, one can easily deviate from the Right Path at any moment.
That is precisely why even the Messenger of Allah (peace be upon him) would constantly supplicate his Lord Most Gracious to save his heart from turning towards evil and keep it steadfast towards the Path of Allah, for it is Allah Subhanah Alone Who has the Absolute Power to control the hearts of His slaves.