Al-Kāfi - The Book of Prayer

Chapter: Salah (Prayer) on a Ship َّدُ بْنُ يَحْيَى عَنْ ٠َّدِ بْنِ الْحُسَيْنِ عَنْ يَزِيدَ بْنِ إِسْحَاقَ عَنْ هَارُونَ بْنِ حَ٠ْزَةَ الْغَنَوِيِّ عَنْ أَبِي عَبْدِ الله (عَلَيْهِ الْسَّلا٠) قَالَ سَأَلْتُهُ عَنِ الصَّلاَةِ فِي السَّفِينَةِ فَقَالَ إِذَا كَانَتْ ٠َّلَةً ثَقِيلَةً إِذَا قُ٠ْ تَحَرَّكْ فَصَلِّ قَائِ٠اً وَإِنْ كَانَتْ خَفِيفَةً تَكَفَّأُ فَصَلِّ قَاعِداً.

He (the Imam) said, ‘If it is heavily loaded and when you stand up it does not shake, perform Salah (prayer) in a standing position, but if it is light that can turn upside down, then perform Salah (prayer) in a sitting position.’” صحيح على الظاهر - Allamah Baqir al-Majlisi (Mirʾāt al-ʿUqūl fī Sharḥ Akhbār Āl al-Rasūl (5/395))