It is narrated from Sayyiduna Abu Umamah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "There are no people who sit in a gathering and then rise from it without having remembered Allah and without having sent blessings upon the Prophet (peace and blessings be upon him), except that the gathering will be a cause of regret and loss for them."
Hadith Referenceالمعجم الكبير للطبراني / باب الصاد / 7720