Abstract:
The Qur’an describes the Day of Resurrection as a mashhad, which means a place, time or stage of witnessing (11:103, 19:37). It is by essence when the truth and hidden realities are disclosed (10:30, 86:9,
100:10). This is a central quality of that Day, by which the Qur’an has sworn (85:3). Whereas one’s book of deeds is his own soul (17:13-14), witnesses are external beings that have encompassed one’s deeds. Therefore, witnesses will complement the records of deeds as they both relate to the process of judgement of individuals in the Hereafter.
Machine summary:
"Based on the above, testimony on the Day of Judgement is the disclosure of some act, belief, or trait through the means and instruments that had some existential presence, observation, and comprehension of that reality in this world.
The record of deeds According to the Qur’an there are guardian angels assigned to each individual, who record the person’s thoughts, acts, and speeches: "Indeed Our messengers write down what you plot" (10:21); "Do they suppose that We do not hear their secret thoughts and their secret talks?
And with them are Our messengers, writing down" (43:80); "there is a guard [or ‘watcher’] over every soul" (86:4); "Indeed, there are over you watchers, noble writers, who know whatever you do" (82:10-12); "When the twin recorders record [his deeds], seated on the right hand and on the left: he says no word but that there is a ready observer beside him" (50:17-18).
The soul as a depository The Qur’an describes this in the following verses: We have attached every person’s omen to his neck, and We shall bring it out for him on the Day of Resurrection as a wide open book that he will encounter.
Another similar usage is found in this verse: "The day We shall summon every group of people with their imām, then whoever is given his book in his right hand – they will read it, and they will not be wronged so much as a single date-thread" (17:71)."