Caution: Translations of Quran and Ḥadīth may lead to possible misapplications and misinterpretations. This site is intended for students of sacred knowledge that are proficient in comprehending classical Arabic and have a strong foundation in Islamic sciences. Also note that religious injunctions rely on several aspects beyond what one may glean through reading individual aḥādīth.
tirmidhi:3587ʿUqbah b. Mukram > Saʿīd b. Sufyān al-Jaḥdarī > ʿAbdullāh b. Maʿdān > ʿĀṣim b. Kulayb al-Jarmī from his father from his grandfather

“I entered upon the Prophet ﷺ while he was praying and he had placed his left hand on his left thigh, and he had placed his right hand on his right thigh, and clasped his fingers, and extended his index finger, and he was saying: ‘O changer of the hearts, make my heart firm upon Your religion (Yā muqallibal-qulūbi thabbit qalbī ʿalā dīnik).’”  

Abū ʿĪsá said that this Ḥadīth is Gharīb in this particular context.
الترمذي:٣٥٨٧حَدَّثَنَا عُقْبَةُ بْنُ مُكْرَمٍ حَدَّثَنَا سَعِيدُ بْنُ سُفْيَانَ الْجَحْدَرِيُّ حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مَعْدَانَ أَخْبَرَنِي عَاصِمُ بْنُ كُلَيْبٍ الْجَرْمِيُّ عَنْ أَبِيهِ عَنْ جَدِّهِ قَالَ

دَخَلْتُ عَلَى النَّبِيِّ ﷺ وَهُوَ يُصَلِّي وَقَدْ وَضَعَ يَدَهُ الْيُسْرَى عَلَى فَخِذِهِ الْيُسْرَى وَوَضَعَ يَدَهُ الْيُمْنَى عَلَى فَخِذِهِ الْيُمْنَى وَقَبَضَ أَصَابِعَهُ وَبَسَطَ السَّبَّابَةَ وَهُوَ يَقُولُ يَا مُقَلِّبَ الْقُلُوبِ ثَبِّتْ قَلْبِي عَلَى دِينِكَ  

قَالَ أَبُو عِيسَى هَذَا حَدِيثٌ غَرِيبٌ مِنْ هَذَا الْوَجْهِ