Musnad Ahmad 26:528

Hashim narrated to us, he said: Al-‘Awwam informed us, from Muhammad ibn Abi Muhammad, a freed slave of ‘Umar ibn al-Khattab, from Abu ‘Ubaydah, and he mentioned its meaning, except that he said: "Abu Dharr said: 'I have not sent ahead except two.'" And likewise, Yazid narrated it to us, and he said: "Abu Dharr said: 'Two have passed on before me.'"