During the first Rak‘ah of the Fajr prayer, I fell asleep in the first prostration and did not wake up until the second. Therefore, I performed only one prostration in the first Rak‘ah and not two: what should I do? Should I perform this Fajr prayer again? Is expiation due, given that this was a long time ago?
All perfect praise be to Allaah, The Lord of the worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
If by saying "a long time ago", you meant that you had not reached puberty at that time (and become competent for religious assignments), then there is no blame on you. However, you should pay greater attention to observing the prayers in the future since you will not be held accountable for what you did before reaching puberty. The Prophet, sallallaahu ‘alayhi wa sallam, said: "The pen does not record the deeds of three people (i.e. they will not be responsible for their actions): the one asleep until he awakens, the insane until he is sane and the child until the age of puberty." [Ahmad, Abu Daawood, An-Nasaa'i, At-Tirmithi and Ibn Maajah]
If you had reached puberty at that time, then your prayer is considered invalid and you should perform it again. The reason for the invalidity of this prayer is because you did not perform one of the two prostrations and they are obligatory according to the consensus of Muslim scholars and the Sunnah. The Prophet, sallallaahu ‘alayhi wa sallam, said to the person who did not perform his prayer properly: "… Then prostrate until you feel at ease in the prostration …" [Al-Bukhari and Muslim]
Another reason for the invalidity of your prayer could be because you had fallen asleep in it, and if it was a deep sleep this invalidates ablution. The Prophet, sallallaahu ‘alayhi wa sallam, said: "The eyes are the drawstrings of the anus, so one who sleeps should perform ablution." [Abu Daawood, Ibn Maajah and Ahmad]
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