What is the ruling on praying behind a latecomer who is praying alone, with the intention of a regular Sunnah prayer and the intention of giving charity?

It is permissible to pray the regular Sunnah (supererogatory) prayer behind someone performing a Fard (obligatory) prayer, with the intention of bestowing charity upon the individual praying alone so that they may attain the reward of congregational prayer. An-Nawawi mentioned in "Al-Majmu'" the permissibility of a person performing a supererogatory prayer and a person performing an obligatory prayer praying behind someone performing a supererogatory prayer and someone performing another obligatory prayer. This is the view of Tawus, 'Ata', Al-Awza'i, Ahmad, Abu Thawr, and Dawud. However, some groups prohibited this, or detailed the permissibility and prohibition.