Was the Prophet the first to narrate the story of the monk Bahira to the Companions, or was it someone else who traveled with him to ash-Sham?

"We discussed the story of Bahira the monk, and Al-Albani authenticated it, saying: 'It is authentic, but the mention of Bilal in it is objectionable.' This story was narrated by Abu Musa al-Ash'ari, and he was not actually present for it. However, the mursal narrations of the Companions are considered authentic and connected by the scholars of hadith (definition) terminology."