The prayer was called to begin while the Messenger of Allah ﷺ was conversing privately with a man in the mosque, and he did not rise for the prayer until the people had already stood up.
حدثنا إسماعيل حدثنا عبد العزيز
أقيمت الصلاة ورسول الله ﷺ نجي لرجل في المسجد فما قام إلى الصلاة حتى قام القوم
Its isnad is sahih. The hadith was narrated by Bukhari 2/124 no. 642, in the chapter on the adhan, when the imam is delayed by some matter, and Muslim 1/284 no. 376, in the chapter on menstruation, evidence that the sleep of one sitting does not invalidate wudu, and Abu Dawud 1/52 no. 201, in the chapter on purification, on wudu after sleep, and Tirmidhi 2/404 no. 526, who said, hasan sahih.