Abu Hurairah (Radia-Allaahu ‘anhu) narrated that Allaah’s Messenger (Salla-Allaahu ‘alayhi wa sallam) said: “If one of you gets up to pray at night and falters in his recitation of Qur’an (i.e. it becomes difficult to recite correctly), and does not know what he is saying, let him lie down.” [Muslim no. 787]
An-Nawawi (Rahimahullaah) said: “The reason behind the abstinence from reciting is explained by Allaah’s Messenger (Salla-Allaahu ‘alayhi wa sallam) in the narration of ‘Aishah (Radia-Allaahu ‘anha)- the mother of the believers- when he (Salla-Allaahu ‘alayhi wa sallam) said: ‘If one of you becomes sleepy while praying, let him sleep until sleep goes away from him, for if one of you prays while he is sleepy, he may intend to pray for forgiveness, but end up impugning (abusing) himself.’ [Muslim no. 786].” [Sharh Muslim by An-Nawawi]
This is a very gentle guidance shown by the Prophet (Salla-Allaahu ‘alayhi wa sallam). Therefore, the reciter of the Qur’an and the one who offers the Salaat are commanded to stop (abstain from) praying and reciting the Qur’an while dozing, because he does not know whether he may be asking pardon or vilifying himself while he does not perceive it. Also, this is to protect the Qur’an from unclear speech and jabber, such that one utters a word wrongly and changes (twists) the meaning.
Since peace of mind and concentration are essential for offering Salaat, it should be offered when one is fresh and free from tiredness and drowsiness. These two Ahadeeth clearly state the reason Muslims have been prohibited from offering Salaat when they are overwhelmed by sleep. Under such conditions, one cannot make a proper expression of one’s humility before Allaah, which is the essence of Salaat.
Therefore, in such conditions, one should first have some sleep, because only then one will get real pleasure from the recitation of the Noble Qur’an, prayer and praise of Allaah, and will be in a position to beseech Him earnestly for pardoning one’s sins. [Commentary on the Hadeeth by As-Sana’ani]
Thus, one should not strain himself, but go back to sleep until drowsiness leaves him whereupon he can resume the night prayer. In the case that Fajr rises, then one can make up the Witr at Duhaa time, but as ‘Shaf’’ (i.e. two-Rak’ah followed by two) in even number. [Ibn ‘Uthaimeen in Riyadus-Saliheen]
Note: It is incumbent upon the reciter of the Qur’an to hold back from reciting if he starts yawning. This is because if one continues reciting while yawning, he may utter a noisy, funny speech (words) and voice. And Allaah’s Speech should be respected and protected from that.
The desirability (recommendation) of continuous recitation without cutting it off
One of the manners which is recommended for the reciter of the Qur’an to act upon is that if he starts reciting the Qur’an, he should not cut it off except for a genuine accidental matter. This is a manner towards the Speech of Allaah i.e. it should not be cut off by worldly matters.
One wonders at those who are waiting to establish the Salaat in congregation in the Masjid. They cut off their recitation many times for worldly reasons which are not important. One should know, the Shaytaan never wants the good for the Muslims!
Al-Bukhaari reported on the authority of Nafi’, the freed slave of Ibn ‘Umar: “Whenever Ibn ‘Umar (Radia-Allaahu ‘anhuma) recited the Qur’an, he would not speak to anyone till he had finished his recitation. Once I held the Qur’an and he recited Surat Al-Baqarah from his memory and then stopped at a certain verse and said: ‘Do you know in what connection this verse was revealed?’ Nafi’ replied: ‘No.’ He said: ‘It was revealed in such and such connection.’ Ibn ‘Umar (Radia-Allaahu ‘anhuma) then resumed his recitation.” [Al-Bukhaari no. 4526]
It was the habit of Ibn ‘Umar (Radia-Allaahu ‘anhuma) not to stop his reciting except for the sake of imparting knowledge, which is also another act of worship.
Sources:
Kitab Al-Adaab by Fu’ad ibn Abdul-Azeez Al-Shalhoob
Sharh Riyad-us-Saliheen by Ibn Uthaimeen.