Allah said,
وَالْوَزْنُ
(And the weighing), of deeds on the Day of Resurrection,
الْحَقِّ
(will be the true (weighing)), for Allah will not wrong anyone. Allah said in other Ayat,
وَنَضَعُ الْمَوَزِينَ الْقِسْطَ لِيَوْمِ الْقِيَـمَةِ فَلاَ تُظْلَمُ نَفْسٌ شَيْئاً وَإِن كَانَ مِثْقَالَ حَبَّةٍ مِّنْ خَرْدَلٍ أَتَيْنَا بِهَا وَكَفَى بِنَا حَـسِبِينَ
(And We shall set up the Balances of justice on the Day of Resurrection, then none will be dealt with unjustly in anything. And if there be the weight of a mustard seed, We will bring it. And Sufficient are We to take account.)21:47,
إِنَّ اللَّهَ لاَ يَظْلِمُ مِثْقَالَ ذَرَّةٍ وَإِن تَكُ حَسَنَةً يُضَـعِفْهَا وَيُؤْتِ مِن لَّدُنْهُ أَجْراً عَظِيماً
(Surely, Allah wrongs not even the weight of a speck of dust, but if there is any good (done), He doubles it, and gives from Him a great reward.) 4:40,
فَأَمَّا مَن ثَقُلَتْ مَوَزِينُهُ فَهُوَ فِى عِيشَةٍ رَّاضِيَةٍ وَأَمَّا مَنْ خَفَّتْ مَوَزِينُهُ فَأُمُّهُ هَاوِيَةٌ وَمَآ أَدْرَاكَ مَا هِيَهْ نَارٌ حَامِيَةٌ
(Then as for him whose scale (of good deeds) will be heavy. He will live a pleasant life (in Paradise). But as for him whose scale (of good deeds) will be light. He will have his home in Hawiyah (pit, Hell). And what will make you know what it is (It is) a fiercely blazing Fire!) 101:6-11 and,
فَإِذَا نُفِخَ فِى الصُّورِ فَلاَ أَنسَـبَ بَيْنَهُمْ يَوْمَئِذٍ وَلاَ يَتَسَآءَلُونَ - فَمَن ثَقُلَتْ مَوَزِينُهُ فَأُوْلَـئِكَ هُمُ الْمُفْلِحُونَ - وَمَنْ خَفَّتْ مَوَزِينُهُ فأُوْلَـئِكَ الَّذِينَ خَسِرُواْ أَنفُسَهُمْ فِى جَهَنَّمَ خَـلِدُونَ
(Then, when the Trumpet is blown, there will be no kinship among them that Day, nor will they ask of one another. Then, those whose scales (of good deeds) are heavy, they are the successful. And those whose scales (of good deeds) are light, they are those who lose themselves, in Hell will they abide)23:101-103. As for what will be placed on the Balance on the Day of Resurrection, it has been said that the deeds will be placed on it, even though they are not material objects. Allah will give these deeds physical weight on the Day of Resurrection. Al-Baghawi said that this was reported from Ibn `Abbas. It is recorded in the Sahih that Al-Baqarah (chapter 2) and Al `Imran (chapter 3) will come on the Day of Resurrection in the shape of two clouds, or two objects that provide shade, or two lined groups of birds. It is also recorded in the Sahih that the Qur'an will come to its companion (who used to recite and preserve it) in the shape of a pale-faced young man. He will ask (the young man), "Who are you" He will reply, "I am the Qur'an, who made you stay up sleeplessly at night and caused you thirst in the day. " The Hadith that Al-Bara' narrated about the questioning in the grave states,
«فَيَأْتِي الْمُؤْمِنَ شَابٌّ حَسَنُ اللَّوْنِ طَيِّبُ الرِّيحِ فَيَقُولُ: مَنْ أَنْتَ؟ فَيَقُولُ: أَنَا عَمَلُكَ الصَّالِح»
(A young man with fair color and good scent will come to the believer, who will ask, `Who are you' He will reply, `I am your good deeds'). The Prophet mentioned the opposite in the case of the disbeliever and the hypocrite. It was also said that the Book of Records that contains the deeds will be weighed. A Hadith states that a man will be brought forth and ninety-nine scrolls containing errors and sins will be placed on one side of the balance each as long as the sight can reach. He will then be brought a card on which `La ilaha illallah' will be written. He will say, "O Lord! What would this card weigh against these scrolls" Allah will say, "You will not be wronged." So the card will be placed on the other side of the Balance, and as the Messenger of Allah ﷺ said,
«فَطَاشَتِ السِّجِلَّاتُ وَثَقُلَتِ الْبِطَاقَة»
(Behold! The (ninety-nine) scrolls will go up, as the card becomes heavier.) At-Tirmidhi recorded similar wording for this Hadith and said that it is authentic. It was also said that the person who performed the deed will be weighed. A Hadith states,
«يُؤْتَى يَوْمَ الْقِيَامَةِ بِالرَّجُلِ السَّمِينِ فَلَا يَزِنُ عِنْدَ اللهِ جَنَاحَ بَعُوضَة»
(On the Day of Resurrection, a fat man will be brought forth, but he will not weigh with Allah equal to the wing of a mosquito). He then recited the Ayah,
فَلاَ نُقِيمُ لَهُمْ يَوْمَ الْقِيَـمَةِ وَزْناً
(And on the Day of Resurrection, We shall assign no weight for them) 18:105. Also, the Prophet said about `Abdullah bin Mas`ud,
«أَتَعْجَبُونَ مِنْ دِقَّةِ سَاقَيْهِ وَالَّذِي نَفْسِي بِيَدِهِ لَهُمَا فِي الْمِيزَانِ أَثْقَلُ مِنْ أُحُد»
(Do you wonder at the thinness of his legs By He in Whose Hand is my soul! They are heavier on the Balance than (Mount) Uhud.) It is also possible to combine the meanings of these Ayat and Hadiths by stating that all this will truly occur, for sometimes the deeds will be weighed, sometimes the scrolls where they are recorded will be weighed, and sometimes those who performed the deeds will be weighed. Allah knows best.