The chain of transmission is ḥasan, and al-Tirmidhī remarks: “A ḥadīth that is ḥasan ṣaḥīḥ.”

2 – Ibn Luhayʿah relates through Mūsā ibn Wardān, from Abū Saʿīd al-Khudrī, that he said:
“We were with the Messenger of Allah ﷺ on a Friday when a Bedouin entered while the Messenger of Allah ﷺ was on the pulpit. The Bedouin sat at the back of the congregation, so the Prophet ﷺ asked him, ‘Have you prayed two rakʿahs?’ He replied, ‘No.’ The Prophet then instructed him, whereupon the man went to the courtyard beside the pulpit and performed two rakʿahs.”

Aḥmad records this report, and its isnād is ḥasan for corroborative and supporting narrations.

Al-Tirmidhī further comments: “Some scholars act upon this ḥadīth; it is the position of al-Shāfiʿī, Aḥmad, and Isḥāq. Others say that if a person enters while the imam is delivering the sermon he should sit and not pray. This is the view of Sufyān al-Thawrī and the scholars of Kūfah, but the first opinion is sounder.”

I add: The same verdict was given by al-Dārimī, the author of the Sunan, and—as al-Tirmidhī stated—it is indeed the stronger view. Imām al-Ṭaḥāwī, however, strove at length to reject this explicit text, and the strongest piece of transmitted evidence he could muster was his statement: “When you say …”