حَدَّثَنَا الْقَعْنَبِيُّ عَنْ مَالِکٍ عَنْ زَيْدِ بْنِ أَسْلَمَ عَنْ عَطَائِ بْنِ يَسَارٍ أَنَّ رَسُولَ اللَّهِ صَلَّی اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ إِذَا شَکَّ أَحَدُکُمْ فِي صَلَاتِهِ فَلَا يَدْرِي کَمْ صَلَّی ثَلَاثًا أَوْ أَرْبَعًا فَلْيُصَلِّ رَکْعَةً وَلْيَسْجُدْ سَجْدَتَيْنِ وَهُوَ جَالِسٌ قَبْلَ التَّسْلِيمِ فَإِنْ کَانَتْ الرَّکْعَةُ الَّتِي صَلَّی خَامِسَةً شَفَعَهَا بِهَاتَيْنِ وَإِنْ کَانَتْ رَابِعَةً فَالسَّجْدَتَانِ تَرْغِيمٌ لِلشَّيْطَانِ
سنن ابودوٗد · Hadith 1026
Narrated Ata ibn Yasar: The Prophet ﷺ said: When one of you is in doubt about his prayer, and does not know how much he has prayed, three or four rak'ahs, he should pray one (additional) rak'ah and make two prostrations while sitting before giving the salutation. If the (additional) rak'ah which he prayed is the fifth one, he will make it an even number by these two prostrations. If it is the fourth one, the two prostrations will be a disgrace for the devil.
Translated by Dr. Muhammad Muhsin Khan · Reviewed by Islamic University of Madinah · Published March 2020