Quran 16:124 · An-Nahl

For all the followers of the prophets, one day of the week has been specified for congregational prayer. The Jews celebrate it on Saturday (the Sabbath), the Christians on Sunday and Muslims have been given orders to arrange for it on Friday. The leading lights among the ancient Jews did some hair-splitting and devised new regulations for the Sabbath. In this way, they bound themselves by artificial restrictions. Thereafter, when they found it impossible to follow those restrictions, they could not reject them in consideration of the holiness of their great men. But, in practice, they started going against these restrictions. The differences created in God’s religion by later scholars and other luminaries by means of their commentaries are not going to be resolved in the world, but when the Day of Judgement comes, God will then show what the real religion of God was and what the things were that the people themselves added to and included in their religion.