The Prayer of Fear, Pursuit, Encounter, and Competition
Man Lā Yaḥḍuruh al-Faqīh|Volume 1|Book 1|Chapter 63
وَ قَالَ: «مَنْ صَلَّى اَلْمَغْرِبَ فِي خَوْفٍ بِالْقَوْمِ صَلَّى بِالطَّائِفَةِ اَلْأُولَى رَكْعَةً وَ بِالطَّائِفَةِ اَلثَّانِيَةِ رَكْعَتَيْنِ.
Imam عليه السلام said : "Whoever prays the Maghrib prayer during a situation of fear with a group, he prays one rak'ah with the first group and two rak'ahs with the second group."
- Ṣaḥīḥ al-Faqīh