Completing the Prayer Behind a Traveling Imam Who Concludes with Three Takbirs

Question:
The questioner says: We prayed the midday prayer in a state of travel behind an imam who shortened the prayer. He stood for the third unit, and we thought he would complete the prayer, but he concluded the prayer after three units. We told him to complete four units, but he refused, even though we had been reciting the remembrance of Allah when he stood for the third unit. I stood up and prayed the fourth unit. Is my prayer valid?

Answer:
There is no harm; it is valid. A traveler has the choice to shorten the prayer or to complete it. He came to the third unit in a state of forgetfulness, so it would have been better for him to perform the prostration for forgetfulness. Otherwise, he is not required to perform the prostration for forgetfulness, because if he had completed the prayer, there would be no harm. Praise be to Allah. If he had completed the third unit as a fourth, there would be no blame on him. However, since he stood up in error, it would be better for him to perform the prostration for forgetfulness, because he came to it in a state of forgetfulness.