Muhammad ibn Yaqub from Muhammad ibn Yahya from Muhammad ibn al-Husayn from Yazid ibn Ishaq from Harun ibn Hamzah al-Ghanawi from Abu Abdillah عليه السلام, peace be upon him. He said: I asked Imam al-Sadiq عليه السلام about prayer on a boat. Imam عليه السلام said: “If it is loaded and heavy, such that when you stand in it, it does not sway, then pray standing. But if it is light and sways, then pray sitting.”