Is it permissible to pray Fajr with Dhuhr?

It is not permissible to delay the prayer beyond its prescribed time without a valid excuse, such as sleep or forgetfulness. If the delay was due to forgetfulness or sleep, then there is no harm in praying Fajr with Dhuhr, based on the Prophet's (peace be upon him) saying: "Whoever oversleeps or forgets a prayer, let him pray it when he remembers it; there is no expiation for it except that."