Chapter on the Detailed Explanation of Prayer, Including the Obligatory and Recommended, and What is Permissible and Not Permissible.

From al-Husayn ibn Sa’id, from Abdullah ibn Bahr, from Hariz, from Muhammad ibn Muslim, who said: I asked Abu Abdillah عليه السلام about a man who feels lazy or weak and prays the recommended (‘nafl’) prayer while sitting. Imam عليه السلام said: "He should double, two rak’ahs in place of one."