A Nestorian monk whom Muhammad met when he was journeying back from Syria to Makkah, and who is said to have perceived by various signs that he was a prophet. His Christian name is supposed to have been Sergius (or Georgius).
Sprenger thinks that Bahira remained with Muhammad, and it has been suggested that there is an allusion to this monk in the Qur’an. Surah xvi. 105: “We know that they say, ‘it is only a man who teacheth him'”. Husain the commentator says on this passage that the Prophet was in the habit of going every evening to a Christian to hear the Taurat and Injil. Tafsir-I-Husaini; Sale, p. 228; Muir’s Life of Mahomet, p 72).
Based on Hughes, Dictionary of Islam