The Prayer of Fear, Pursuit, Encounter, and Competition
Man Lā Yaḥḍuruh al-Faqīh|Volume 1|Book 1|Chapter 63
وَ رَوَى عَبْدُ اَلرَّحْمَنِ بْنُ أَبِي عَبْدِ اَللَّهِ عَنِ اَلصَّادِقِ عَلَيْهِ اَلسَّلاَمُ: فِي صَلاَةِ اَلزَّحْفِ قَالَ «تُكَبِّرُ وَ تُهَلِّلُ يَقُولُ اَللَّهُ عَزَّ وَ جَلَّ: «فَإِنْ خِفْتُمْ فَرِجٰالاً أَوْ رُكْبٰاناً ».
Abd al-Rahman ibn Abi Abdullah reported from Imam Jafar ibn Muhammad Al-Sadiq عليه السلام regarding the prayer during advancing troops (battle or combat). Imam عليه السلام said: "You say the takbir (proclaiming 'Allahu Akbar') and tahleel (proclaiming 'La ilaha illa Allah سبحانه وتعالى'). Allah سبحانه وتعالى, the Mighty and Majestic, says: 'But if you fear [an enemy], then [pray] on foot or while riding' (Surah Al-Baqarah 2:239)”.
- Ṣaḥīḥ al-Faqīh, p. 67