Sayyiduna Zayd bin Thabit (may Allah be pleased with him) said: I was sitting at the side of the Messenger of Allah (peace and blessings be upon him), with my thigh beneath his (peace and blessings be upon him) thigh, and he (peace and blessings be upon him) was dictating this verse to me: "Not equal are those of the believers who sit back and those who strive in the way of Allah with their wealth and their lives" [Surah al-Nisa: 95]. Ibn Umm Maktum (may Allah be pleased with him) was sitting and listening, and he said: By Allah! O Prophet of Allah, if I had the strength for jihad, I would certainly strive in jihad. Thereupon Allah sent down Qur'an upon His Messenger (peace and blessings be upon him) concerning this, and his (peace and blessings be upon him) thigh became so heavy on my thigh that I thought it would be crushed. Then the state of revelation lifted from him (peace and blessings be upon him), and he said: "Not equal are those of the believers who sit back, except those who are disabled" [Surah al-Nisa: 95].
Hadith Referenceالمعجم الكبير للطبراني / باب الزاي / 4798