Order between old and new missed prayers

Question

Zayd, on reaching the twentieth year of his life, repents. During this period he sometimes prayed and sometimes did not, so he estimated [the missed] prayers approximately and began making up the prayers missed over a lifetime. It so happened that one of his prayers was missed (became qada'). Should he now first make up this prayer that became qada', or make it up only when all his earlier prayers have been made up? If he makes up the new missed prayer first, will it be valid or not?

Answer

He should make up this new missed prayer as well, without waiting for [the making up of] the prayers of the past periods.

Source: Fatawa Mahmudiyya

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