This imam has been leading prayers in the mesjid for years. In fajr, salat al-jumuah, and the first 2 rak'ahs of maghrib and isha, he does recite with tajweed. But one time, in the third rak'ah of maghrib if I remember correctly, as he was reciting surah al-fatiha, he recited a little bit louder than usual, so the microphone got his words and then all the sound emitters in the mesjid spread his recitation. We heard him say (الضَّالِّينَ) without any madd. All the scholars are agreed the there's madd lazm (مد لازم) on the alif in (الضَّالِّين), so it must be lengthened to 6 harakat (in Hafs 'an Assim). Is it permissible to pray behind this imam?