Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) prayed Fajr in one of the mosques of Banu Asad, and their imam led them in prayer reciting the two longest surahs of the Mufassal according to the arrangement of Sayyiduna Abdullah (may Allah be pleased with him). When the prayer was completed, Sayyiduna Abdullah (may Allah be pleased with him) said: "What is this, that I see you a young man, and you recite these two surahs in this prayer, while you are a young man?"
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 9158