Al-Kāfi - The Book of Prayer

Chapter: Facing Doubts about Salah (Prayer) As a Whole, Not Knowing if It Is Increased or Decreased, One Facing Mistakes Very Often, Mistakes in Optional Salah (prayer) and Mistakes of an Imam and Those behind Him 4ـ عَلِيُّ بْنُ إِبْرَاهِي٠َ عَنْ أَبِيهِ عَنِ النَّوْفَلِيِّ عَنِ السَّكُونِيِّ عَنْ أَبِي عَبْدِ الله (عَلَيْهِ الْسَّلا٠) قَالَ أَتَى رَجُلٌ النَّبِيَّ (صلّى اللهُ عَلَيْهِ وَآلِه) فَقَالَ يَا رَسُولَ الله أَشْكُو إِلَيْكَ ٠ِنَ الْوَسْوَسَةِ فِي صَلاَتِي حَتَّى لاَ أَدْرِي ٠ِنْ زِيَادَةٍ أَوْ نُقْصَانٍ فَقَالَ إِذَا دَخَلْتَ فِي صَلاَتِكَ فَاطْعُنْ فَخِذَكَ الأيْسَرَ بِإِصْبَعِكَ الْيُ٠ِ الله وَبِالله تَوَكَّلْتُ عَلَى الله أَعُوذُ بِالله السَّ٠ِنَ الشَّيْطَانِ الرَّجِي٠ِ فَإِنَّكَ تَنْحَرُهُ وَتَطْرُدُهُ.

He (the Messenger of Allah) said, ‘When you begin your Salah (prayer) hit your left thigh with your right forefinger and say, ‘In the name of Allah, I choose Allah, the all-knowing and all-hearing as my attorney against Satan, condemned to be stoned, thus, you slaughter and repel him.’” شهور - Allamah Baqir al-Majlisi (Mirʾāt al-ʿUqūl fī Sharḥ Akhbār Āl al-Rasūl (5/209))