Sahih al-Bukhari 3875
صحيح البخاري#3875SahihNarrated `Abdullah:We used to greet the Prophet (ﷺ) while he used to be in prayers, and he used to reply to our greetings. But when we came back from Najashi (the King of Ethiopia) we greeted him (while he was praying) and he did not reply to us. We said, "O Allah's Messenger (ﷺ)! We used to greet you in the past and you used to reply to us." He said, "Verily The Mind is occupied and busy with more important matter during the prayer." (So one cannot return One's greetings)
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Every narration in Sahih al-Bukhari is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 63:100