Mukhtasar Sahih Bukhari — Hadith 1212

It is narrated from Sayyiduna Jundub bin Sufyan, may Allah be pleased with him, that the Messenger of Allah, peace and blessings be upon him, was in a battle when his finger became wounded and bloodied. So the Prophet, peace and blessings be upon him, said: "You are but a finger that has become bloodied, and this calamity you have borne is in the way of Allah."