Prayer on a Ship
Man Lā Yaḥḍuruh al-Faqīh|Volume 1|Book 1|Chapter 62
وَ سَأَلَ زُرَارَةُ أَبَا جَعْفَرٍ عَلَيْهِ اَلسَّلاَمُ: فِي اَلرَّجُلِ يُصَلِّي اَلنَّوَافِلَ فِي اَلسَّفِينَةِ قَالَ «يُصَلِّي نَحْوَ رَأْسِهَا.
Zurarah asked Imam Muhammad ibn Ali Al-Baqir عليه السلام about a man performing supererogatory (nafilah) prayers on a ship. Imam عليه السلام said: "He should pray in the direction of its front (bow)."
- Ṣaḥīḥ al-Faqīh, p. 66