How can one make up for missed prayers, perform ghusl for ritual impurity, and repent before the month of Ramadan, given that the number of missed prayers is unknown?

Some scholars and Companions held the view that one who abandons prayer is an unbeliever, a disbeliever who has exited the fold of Islam, based on the Prophet's (peace and blessings be upon him) saying: "Between a person and disbelief and polytheism is the abandonment of prayer." The one who abandons prayer must repent to Allah, and he is not required to make up the missed prayers. However, making up what was missed is more cautious and absolves one's responsibility. As for ghusl (ritual bath), it is sufficient to perform ghusl for janabah (ritual impurity) when it occurs and to promptly pray at its prescribed time, as janabah is not an excuse for abandoning prayer or delaying it.