Is it obligatory to make up prayers missed intentionally or by oversight before the prescribed prayer, and are prayers performed before making up the missed ones unacceptable?

The Hanafis and Hanbalis are of the view that it is obligatory to observe the order between missed prayers and the current obligatory prayer. They cite the Prophet's (peace be upon him) saying: "Whoever forgets a prayer or sleeps through it, its expiation is to pray it when he remembers it." The Malikis hold that observing the order is obligatory if the missed prayers are few (four or five); however, for six or more, observing the order with the current prayer is not obligatory. They stipulate observing the order for the validity of a second prayer that shares the same time as the first. The Shafi'is, on the other hand, are of the view that observing the order is only recommended. Generally, missed prayers are to be offered before the current prayer, whether obligatorily or preferably. If one reverses the order, their prayer is valid, except for the Malikis if the second prayer shares the same time as the first, such as two Dhuhr prayers or two Isha prayers whose time has not expired, in which case failing to observe the order invalidates the latter of the two.