Musnad Abu Ya'la al-Mawsili 76:3

Abu Abd al-Rahman al-Adhrami narrated to us, Abd al-Aziz ibn Imran narrated to us, from Abd al-Rahman ibn al-Harith ibn Ubayd, from his grandfather, who said: Abu Dharr’s eye was injured on the day of Uhud, so the Prophet, peace and blessings of Allah be upon him, spat into it, and it became the soundest of his two eyes.