Sahih Bukhari, Chapter: Jihaad (Fighting for the cause of Allah)

When the Divine Inspiration: "Those of the believers who sit (at home)..., was revealed the Prophet (SAW) sent for Zaid (bin Thabit) who came with a shoulder-blade and wrote on it. Ibn Um-Maktum complained about his blindness and on that the following revelation came: "Not equal are those believers who sit (at home) except those who are disabled (by injury, or are blind or lame)..." (4.95)