Sayyiduna Imran bin Husain (may Allah be pleased with him) narrates: The Noble Prophet (peace and blessings be upon him) said: "Offering prayer while sitting has half the reward of offering prayer while standing, and offering prayer while lying down has half the reward of offering prayer while sitting."

Sayyiduna Jabir (may Allah be pleased with him) narrates: Once the Prophet Muhammad (peace and blessings be upon him) was riding a horse in Madinah Munawwarah, and he was injured by a date-palm trunk, as a result of which his foot was hurt. He stayed in the house of Sayyidah Aisha (may Allah be pleased with her). We came to visit him and found him performing voluntary prayers while sitting. We stood behind him and prayed. Then, when we came to him (on another occasion), he was performing an obligatory prayer. We stood behind him, so he gestured to us to sit down. When the Prophet (peace and blessings be upon him) completed the prayer, he said: "Follow the Imam. When he performs the prayer sitting, then you also perform the prayer sitting, and when he performs the prayer standing, then you also perform the prayer standing. Do not behave in the manner that the people of Persia do for their elders."

This narration is also transmitted with another chain, however, the word 'nafl' is not mentioned in it.

Ibrahim bin Ubaid reports: I went to the service of Sayyiduna Jabir bin Abdullah (may Allah be pleased with him), and found him leading his companions in prayer while sitting. When he finished the prayer, I asked him about this. He said: "I am actually unable to stand. When you pray behind me, then perform the prayer sitting," because I heard the Prophet Muhammad (peace be upon him) say: "The Imam is a shield; if he prays standing, then you should also pray standing, and if he prays sitting, then you should also pray sitting."