When does the time for the Shafa and Witr prayers end, and is it permissible to delay them until the time of the Fajr takbeer?

The time for Witr prayer extends from after the 'Isha prayer until the break of dawn, based on the Prophet's (peace and blessings be upon him) sayings: "(Perform) Witr before morning," and "Hasten to perform Witr before dawn," and "If dawn breaks, all night prayer and Witr have passed, so perform Witr before dawn breaks." Ibn 'Uthaymin said: "This indicates that the time for Witr ends with the break of dawn." Some scholars have held the view that it is permissible to pray it after dawn until one prays the Fajr prayer, citing the actions of some Companions, but the preponderant opinion is that its time ends with the break of dawn.