The Messenger of Allah ﷺ said, "No people gather in a sitting and then disperse without remembering Allah and sending blessings upon the Prophet ﷺ, except that their gathering will be a source of regret for them on the Day of Resurrection."
حدثنا وكيع عن سفيان عن صالح يعني مولى التوأمة
قال رسول الله ﷺ ما اجتمع قوم في مجلس فتفرقوا ولم يذكروا الله عز وجل ويصلوا على النبي ﷺ إلا كان مجلسهم ترة عليهم يوم القيامة
Its isnad is sahih. As for Salih bin Nabhan, the freedman of Tawama, Shaykh Shakir used to grade his hadith sahih. This hadith occurred earlier at 9029 in the printed edition, and the reason his hadith is graded sahih is that Sufyan's transmission from him came before he became confused in his old age.