Volume 4 · Book 52 · Hadith 58
Narrated Jundab bin Sufyan: In one of the holy Battles a finger of Allah's Apostle (got wounded and) bled. He said, "You are just a finger that bled, and what you got is in Allah's Cause."
— Sahih Bukhari, Volume 4, Book 52: Fighting for the Cause of Allah (Jihaad), Hadith #58