Is it permissible to perform the post-prayer regular Sunnah with another group that is late?

If you wish to pray the post- obligatory Sunnah prayer behind someone performing a fard (obligatory) prayer, there is no objection to this according to the majority of scholars. Al-Nawawi, in "Al-Majmu‘," narrated the permissibility of a person performing a nafl (supererogatory) prayer or a fard prayer praying behind someone performing a nafl prayer or a fard prayer of a different type.