In making up missed prayers (qada'), should we start with the fard (obligatory) or the sunnah (recommended) prayers?

If one misses many obligatory prayers and their associated regular supererogatory prayers, it is incumbent upon him to make up the obligatory prayers, and it is recommended for him to make up the supererogatory ones. It is not valid to make up a post-obligatory supererogatory prayer except after the obligatory prayer. However, it is valid to make up a pre-obligatory supererogatory prayer either before or after the obligatory prayer. If an obligatory prayer is intentionally missed, it is obligatory to hasten to make it up first, because its making up is immediate. If it was missed due to an excuse, then it is preferable to make up the obligatory prayers first, then the supererogatory ones, in order to clear one's liability concerning the obligatory prayers.