Description of the Prayer from Its Beginning to Its End
Man Lā Yaḥḍuruh al-Faqīh|Volume 1|Book 1|Chapter 46
وَ كَانَ رَسُولُ اَللَّهِ صَلَّى اَللَّهُ عَلَيْهِ وَ آلِهِ أَتَمَّ اَلنَّاسِ صَلاَةً وَ أَوْجَزَهُمْ كَانَ إِذَا دَخَلَ فِي صَلاَةٍ قَالَ «اَللَّهُ أَكْبَرُ «بِسْمِ اَللّٰهِ اَلرَّحْمٰنِ اَلرَّحِيمِ».
"The Messenger of Allah صلى الله عليه وعلى آله وسلم was the most complete in performing prayer and the most concise. When he began his prayer, he would say: 'Allāhu Akbar (God is the Greatest)' and then recite, 'Bismillāh al-Raḥmān al-Raḥīm (In the name of Allah سبحانه وتعالى, the Most Gracious, the Most Merciful).'"
- Ṣaḥīḥ al-Faqīh