The Messenger of Allah ﷺ said, "When a servant remains seated in his place of prayer after completing the prayer, the angels send blessings upon him, and their blessing is, 'O Allah, forgive him. O Allah, have mercy on him.' And if he sits waiting for the next prayer, the angels send blessings upon him, and their blessing is, 'O Allah, forgive him. O Allah, have mercy on him.'"
حدثنا يحيى بن آدم حدثنا إسرائيل عن عطاء بن السائب عن أبي عبد الرحمن قال سمعت
قال رسول الله ﷺ إن العبد إذا جلس في مصلاه بعد الصلاة صلت عليه الملائكة وصلاتهم عليه اللهم اغفر له اللهم ارحمه وإن جلس ينتظر الصلاة صلت عليه الملائكة وصلاتهم عليه اللهم اغفر له اللهم ارحمه
Its chain of transmission is hasan. Ata bin Saaib became confused in memory toward the end of his life, and they did not mention Israil bin Yunus among those who heard from him early on, before his confusion set in. Abu Abdul-Rahman is Sulami. The hadith is in Zawaid 2:36.