The ruling on praying the obligatory prayer behind one who is praying the witr

Question:
May Allah reward you. A man says: I was praying the witr in the airport prayer area, when another man came and prayed with me, intending the Fajr prayer. The first man, who was praying the witr, recited aloud, then completed the prayer with an even number of rak'ahs. It is known that he said the opening takbir with the intention of witr. What is the ruling on this prayer? May Allah reward you with good.

Answer:
If he said the opening takbir with the intention of witr, it is not an obligatory prayer. The Messenger (peace and blessings be upon him) said: “Actions are only by intentions.” However, if his intention was that the one who joined him intended witr, while he himself intended the obligatory prayer, there is no harm in that. It is permissible to pray the obligatory prayer behind one who is praying, or with one who is praying, a voluntary prayer, whether witr or other than witr. But he should not make it witr; he should not make his prayer witr. Rather, he stands and completes his prayer.