Congregational Dzikr is a Sunnah

بِسۡمِ ٱللهِ ٱلرَّحۡمَـٰنِ ٱلرَّحِيمِ

Regarding the source of the method of teaching the remembrances, adzkar, and the litanies, awrad; it has been reported by Imam Ahmad ibn Muhammad Hanbal (r.a.) in his Musnad, with an excellent chain of transmission, and by Imam Abu al-Qasim Sulayman ibn Ayyub ath-Thabarani (r.a.) and others, that Hadhrat Ya’la ibn Shaddad (r.a.) said, “My father, Shaddad ibn Aws told me, in the presence of ‘Ubadah ibn asw-Swamit, who said he was telling the truth, ‘We were together with the Prophet (s.a.w.), and he asked, ‘Is there a stranger amongst you?’ meaning one of the People of the Scripture. 

We said, ‘No, O Messenger of Allah,’ so he ordered the door to be locked. 

Then he said, ‘Raise your hands and say, ‘There is no god but Allah!’  So, we held our hands up for a while, then he said, ‘Praise be to Allah!  O Allah, You have Sent me with this declaration.  You have Entrusted me with it, and You have Promised me the Garden of Paradise on account of it, and You will not fail to keep the Promise!’  Then he said, ‘Be of good cheer, for Allah has Granted you Forgiveness!’’”