[Machine] The Messenger of Allah ﷺ said, "I am only a human being, I forget just as you forget. So, whoever doubts his prayer should seek guidance from what iscorrect and complete it. Then, they should prostrate two prostrations."  

قَالَ رَسُولُ اللهِ ﷺ إِنَّمَا أَنَا بَشَرٌ أَنْسَى كَمَا تَنْسَوْنَ فَأَيُّكُمْ شَكَّ فِي صَلَاتِهِ فَلْيَنْظُرْ أَحْرَى ذَلِكَ إِلَى الصَّوَابِ فَلْيُتِمَّ عَلَيْهِ وَيَسْجُدْ سَجْدَتَيْنِ  

Abu Hurairah reported the Messenger of Allah ﷺ as saying; When one of you stands up to pray, the devil comes to him and confuses him so that he does not know how much he has prayed. If any of you has such an experience, he should perform two prostrations while he is sitting. Abu Dawud said; This tradition has been narrated in a similar manner by Ibn ‘Uyainab, Ma’mar and al-Laith. (Using translation from Abū Dāʾūd 1030)   

أَنَّ رَسُولَ اللهِ ﷺ قَالَ إِنَّ أَحَدَكُمْ إِذَا قَامَ يُصَلِّي جَاءَهُ الشَّيْطَانُ فَلَبَّسَ عَلَيْهِ حَتَّى لَا يَدْرِي كَمْ صَلَّى فَإِذَا وَجَدَ أَحَدُكُمْ ذَلِكَ فَلْيَسْجُدْ سَجْدَتَيْنِ وَهُوَ جَالِسٌ  

Messenger of Allah ﷺ said, "When the call for prayer is made, Satan takes to his heels passing wind so that he may not hear the Adhan and when the call is finished he comes back, and when the Iqama is pronounced, Satan again takes to his heels, and when the Iqama is finished he comes back again and tries to interfere with the person and his thoughts and say, "Remember this and that (which he has not thought of before the prayer)", till the praying person forgets how much he has prayed. If anyone of you does not remember whether he has offered three or four rakʿat then he should perform two prostrations of Sahu while sitting. (Using translation from Bukhārī 1231)   

أَنَّ النَّبِيَّ ﷺ قَالَ إِذَا نُودِيَ بِالصَّلَاةِ أَدْبَرَ الشَّيْطَانُ لَهُ ضُرَاطٌ حَتَّى لَا يَسْمَعُ النِّدَاءَ فَإِذَا قُضِيَ النِّدَاءُ أَقْبَلَ فَإِذَا ثُوِّبَ بِهَا أَدْبَرَ فَإِذَا قُضِيَ التَّثْوِيبُ أَقْبَلَ حَتَّى يَخْطِرَ بَيْنَ الْمَرْءِ وَبَيْنَ نَفْسِهِ حَتَّى يَقُولُ اذْكُرْ كَذَا اذْكُرْ كَذَا لِمَا لَمْ يَكُنْ يَذْكُرُ فَإِذَا لَمْ يَدْرِ أَحَدُكُمْ صَلَّى ثَلَاثًا أَوْ أَرْبَعًا فَلْيَسْجُدْ سَجْدَتَيْنِ وَهُوَ جَالِسٌ