It is narrated from Nafi that a man asked Sayyiduna Abdullah bin Umar (may Allah be pleased with them both): "I perform prayer at home, then I find the congregation with the Imam; should I then pray again with the Imam?" Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) said: "Yes." The man asked: "Then, out of the two prayers, which one should I consider as obligatory and which as supererogatory (nafl)?" Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) replied: "What concern is that of yours? That is up to Allah, the Glorious and Exalted; He may make whichever He wills obligatory and whichever He wills supererogatory."