An aspirant asked permission do join one of the senior murid in doing the dhikr at tahajjud.
Hakim al-Umma Hadhrat Mawlana Ashraf ‘Ali Thanawi (may Allah have mercy on him) replied,
“There is nothing wrong if you join him in doing the dhikr. But no third person should join. Otherwise, this will become a customary practice ( to convene for collective dhikr).”
To another similar question Hadhrat Hakim al-Umma replied,
“There is nothing wrong in collective dhikr if done without considering it to be essential or making announcement (for inviting others). Except for Hafidh sahib (and you) there should not be any third person (joining this dhikr).”
Tarbiyet us Salik, volume 2, page 925