It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) concerning the saying of Allah, the Mighty and Majestic: "Not equal are those of the believers who sit (at home) without a disability (and those who strive in the path of Allah)" [Surah al-Nisa: 95]. He said: "These were people in the time of the Messenger of Allah (peace and blessings be upon him) who did not go out on campaigns with him (peace and blessings be upon him) because of illnesses and ailments, and there were others, healthy people, who also did not go out on campaigns with him (peace and blessings be upon him); so the sick were excused, unlike the healthy."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 12720