Zahdam al-Jarmi said: We were sitting with Sayyiduna Abu Musa al-Ash'ari (may Allah be pleased with him) when food was presented to him which contained chicken meat. Among those present was a man from the red Banu Taym Allah, and he did not come near. Sayyiduna Abu Musa (may Allah be pleased with him) said to him: Come closer, for I have seen the Messenger of Allah (peace and blessings be upon him) eating this.
Hadith Referenceسنن دارمي / من كتاب الاطعمة / 2092
This hadith is agreed upon (muttafaqun alayh), from which it is established that eating chicken is permissible, because its entire diet is not filth, and the Messenger of Allah (sallallahu alayhi wa sallam) himself ate chicken meat.
This hadith is mentioned in more detail in Sahih al-Bukhari.
That red and white man from Banu Taym Allah said: I saw that the chicken was eating filth, so I swore an oath that I would not eat chicken.
Sayyiduna Abu Musa (radi Allahu anhu) said: Break your oath and eat it; I have seen the Messenger of Allah (sallallahu alayhi wa sallam) break an oath as well.