Types of Riddah were pointed out earlier; and it is not a condition for it to occur that the Murtad (apostate) says, “I apostatize from Islam.” But if he says so, his statement will be counted as one type of Riddah.
The Murtad who returns to Islam is not required to make up for what he missed during his apostasy of Salah, Sawm, Zakah, etc. Moreover, he will not lose the righteous deeds he had done before committing apostasy if he returns to Islam and dies as a believer. Allah (Exalted be He) makes the loss of righteous deeds in this case dependent upon the person dying as a disbeliever. Allah (Exalted be He) says (what means):
Verily, those who disbelieve, and die while they are disbelievers
He also says:
And whosoever of you turns back from his religion and dies as a disbeliever, then his deeds will be lost in this life and in the Hereafter
As for the vow made at the time a person was a Muslim (before committing apostasy), it continues to be binding as long as it involves an obedience to Allah. (Part No. 2; Page No. 10) A person should fulfill this vow after returning to Islam. He should also fulfill the rights of Allah and the rights of servants that he owed before committing apostasy, for they remain binding.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.