Reference: Fataawa Ramadhaan – Volume 1, Page 200, Fatwa No.141
Question: If the time for Fajr is approaching in Ramadhaan and I need to make ghusl but there is not enough time to perform it nor eat the sahoor, should I perform the ghusl and miss the sahoor or should I eat the sahoor and delay the ghusl until after Fajr?
Response: It is better to eat the sahoor because the Prophet ﷺ said: «Eat the pre-dawn meal (suhoor) for in it is blessing», and delay the ghusl because it’s time is plenty. So, if Fajr has arrived and you have not made ghusl, then make it and pray and your fast will not be affected. It has been confirmed on the authority of ‘Aa.ishah and Umm Salamah (radhi-yAllaahu ‘anhumaa) that: “if the Messenger of Allaah ﷺ entered the time of Fajr whilst in a state of impurity (Junub) from having had relations with his wife, then he used to make ghusl and fast”. [The authenticity of this narration is] agreed upon.