A traveler praying behind a resident Imam

A: Joining a congregation that was offering Maghrib (Sunset) Prayer with the intention of praying ‘Isha’ shortened to two Rak‘ahs (units of Prayer) is not valid because when a traveler offers Salah behind a non-traveling Imam, he must follow him and complete the Salah; shortening Salah is not permissible for him because of the Hadith reported by Musa ibn Salamah: “We were with Ibn ‘Abbas in Makkah, I said, ‘When we are with you, we offer four Rak‘ahs and when we go back to our dwellings, we offer two Rak‘ahs.’ He said, ‘This is the Sunnah (way) of Abu Al-Qasim (i.e. Muhammad peace be upon him).’” (Related by Ahmad, Muslim and others in similar wordings) Consequently, you have to repeat this Salah offering four Rak‘ahs. (Part No. 6; Page No. 465) May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.