The first thing for which a person will be called to account will be his Prayers Sunan Ibn Majah 1425
Arabic hadith text
حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، وَمُحَمَّدُ بْنُ بَشَّارٍ، قَالاَ حَدَّثَنَا يَزِيدُ بْنُ هَارُونَ، عَنْ سُفْيَانَ بْنِ حُسَيْنٍ، عَنْ عَلِيِّ بْنِ زَيْدٍ، عَنْ أَنَسِ بْنِ حَكِيمٍ الضَّبِّيِّ، قَالَ قَالَ لِي أَبُو هُرَيْرَةَ إِذَا أَتَيْتَ أَهْلَ مِصْرِكَ فَأَخْبِرْهُمْ أَنِّي، سَمِعْتُ رَسُولَ اللَّهِ ـ صلى الله عليه وسلم ـ يَقُولُ " إِنَّ أَوَّلَ مَا يُحَاسَبُ بِهِ الْعَبْدُ الْمُسْلِمُ يَوْمَ الْقِيَامَةِ، الصَّلاَةُ الْمَكْتُوبَةُ فَإِنْ أَتَمَّهَا، وَإِلاَّ قِيلَ: انْظُرُوا هَلْ لَهُ مِنْ تَطَوُّعٍ؟ فَإِنْ كَانَ لَهُ تَطَوُّعٌ أُكْمِلَتِ الْفَرِيضَةُ مِنْ تَطَوُّعِهِ. ثُمَّ يُفْعَلُ بِسَائِرِ الأَعْمَالِ الْمَفْرُوضَةِ مِثْلُ ذَلِكَ "
Translation
It wasnarrated that Anas bin Hakim Dabbi said
“Abu Hurairah said tome:‘When you go to your country, tell them that I heard the Messengerof Allah (ﷺ) say: “The first thing for which the Muslim will bebrought to account on the Day of Resurrection will be the prescribedprayers. If they are complete, all well and good, otherwise it willbesaid: ‘Look and see whether he has any voluntary prayers.’ Ifhe hasany voluntary prayers, his prescribed prayers will becompleted fromhis voluntary prayers. Then the same will be done withregard to allhis obligatory deeds.”