Fiqh-us-Sunnah Volume 2, Supererogatory Prayer, Fiqh 2.099.

The scholars agree that it is obligatory for one who has forgotten the salah or slept through its time to make up the missed [qada’) prayer. This opinion is based on the hadith of the Prophet mentioned earlier: “There is no negligence while one is asleep but forgetfulness occurs when one is awake. If one of you forgets the prayer or sleeps through its time, then he should perform the salah when he recalls it.” If one falls unconscious, then he need not repeat the salah, unless he regains his consciousness with enough time to purify himself and perform the salah within its proper time.

‘Abdurrazaq relates from Naf’i that Ibn ‘Umar once fell sick and became unconscious and missed the prayer. When he regained his consciousness, he did not make up the missed prayer.

Ibn Juraij reports from Ibn Tawus on the authority of his father that if a sick person becomes unconscious, he is not to make up the prayers he missed.

Mu’ammar relates: “I asked az-Zuhri about one who becomes unconscious, and he said that he is not to make up the salah he missed.”

Hamad ibn Salamah relates from Yunus ibn ‘Ubaid that both al-Hassan al-Basri and Muhammad ibn Sireen said that a person who falls unconscious is not to make up the prayers he may miss.

Concerning missing a salah intentionally, the majority of the scholars say that it is a sin and the missed salah must be made up for. Ibn Taimaiyyah says: