Is prayer obligatory immediately upon waking in the morning, or can it be made up with Dhuhr prayer?

A Muslim must perform the Fajr prayer immediately upon waking up, and it is not permissible to delay it to perform it with the Dhuhr prayer, due to the Prophet's (peace and blessings of Allah be upon him) saying: "Whoever forgets a prayer or sleeps through it, its expiation is to pray it when he remembers it."