The Messenger of Allah ﷺ said, "One of you remains in a state of prayer as long as he sits in his place waiting for the prayer, and the angels keep saying, 'Allah, forgive him. Allah, have mercy on him,' so long as he does not break his ablution."
حدثنا أبو أحمد حدثنا كثير بن زيد عن الوليد بن رباح
قال رسول الله ﷺ لا يزال أحدكم في صلاة ما دام في مجلسه ينتظر الصلاة والملائكة يقولون اللهم اغفر له اللهم ارحمه ما لم يحدث
Its isnad is sahih. It was mentioned previously at 7603. Kathir bin Zayd is trustworthy, though he has been criticized, but this does not affect his integrity. The hadith is found in Bukhari 1/66, in the book of adhan, chapter on the merit of praying in congregation, and Muslim 1/459 no. 649, in the book of masjids, chapter on the merit of praying in congregation, and Abu Dawud 1/127 no. 470, in the book of prayer, chapter on the merit of sitting in the masjid, and Tirmidhi 2/150 no. 330, in the book of prayer, chapter on what has been said about sitting in the masjid, where he said, hasan sahih.