Jami` at-Tirmidhi 2140
جامع الترمذي#2140Da'ifAnas narrated:"The Messenger of Allah (s.a.w) would often say: Ya Muqallibal-qulub, thabbit qalbi 'ala dinik('O Changer of the Hearts! Strengthen my heart upon Your Religion.)' So I said: 'O Prophet of Allah! We believe in you and what you have come with, but do you fear for us?' He said: 'Yes. Indeed the hearts are between two Fingers of Allah's Fingers, He changes them as He wills
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Ahmad Muhammad ShakirSahih
Al-AlbaniSahih
Zubair Ali ZaiDaif
In-book reference: 32:8