They were a people during the time of the Messenger of Allah ﷺ who did not go out on military expeditions with him due to illnesses, sicknesses, and ailments. Others among them were healthy yet still did not go out with him. The sick were excused, unlike the healthy.
في قوله تعالى: {لا يستوي القاعدون من المؤمنين غير أولى الضرر}
هم قوم كانوا على عهد رسول الله ﷺ لا يغزون معه لأسقام، وأمراض، وأوجاع وآخرون أصحاء لا يغزون معه، وكان المرضي في عذر من الأصحاء.
Tabarani narrated it in Al-Kabir (12/165) through two routes, from Abu Aqeel Dawraqi, from Abu Nadra, from Ibn Abbas, as he mentioned it. Its isnad is sahih. Abu Aqeel Dawraqi is Bashir bin Uqba Naji, one of the men found in the Sahih. Abu Nadra is Munzir bin Malik bin Qita.Haythami said in Al-Majmu (9/7), "Tabarani narrated it through two routes, and the men of one of them are trustworthy."