An imam concluded the prayer with takbir instead of taslim; what is the ruling on his prayer and the prayer of the ma'mums?

Question:
May Allah reward you, Honorable Shaykh. This questioner says: I prayed behind an imam, and in the last rak'ah he did not conclude the prayer with taslim; rather, he was content with saying Allahu Akbar three times, which was in place of the taslim. Is my prayer with him valid, or must I repeat it?

Answer:
Neither your prayer nor his is valid, because taslim is a pillar of the prayer. The prayer begins with takbir and concludes with taslim; it begins with the takbir of ihram and concludes with taslim. The prayer is not valid, so you must repeat your prayer. You should also tell him to repeat his prayer, as well as everyone who prayed behind him, because they left out a pillar of the prayer. Yes.