Should I say the Taslim with the Imam after Maghrib prayer or add another Rak'ah to avoid Witr prayer?

Giving charity by praying with someone who missed the congregational prayer is a good deed, and the Prophet, peace and blessings be upon him, commanded it, as narrated by Imam Ahmad from the Hadith (definition) of Abu Sa'id al-Khudri that the Prophet, peace and blessings be upon him, said, "Who will give charity to this person by praying with him?" This was when a man entered the mosque after the Prophet, peace and blessings be upon him, had already prayed with his companions. The one who gives charity should make his salaam with the Imam's salaam, and there is no objection to his prayer being an odd number of rak'ahs, as Mu'adh used to do.