Ma'arif al-Qur'an
Mufti Muhammad Shafiإِنَّهُ لَحَقٌّ مِّثْلَ مَا أَنَّكُمْ تَنطِقُونَ (...it [ the Day of Recompense ] is a reality, as sure as that you speak....51:23). It means that all of the matters relating to Judgment, Resurrection and Recompense that they have been promised shall certainly occur. Therefore, it is the truth, there being no doubt about it, so they should not doubt its coming, just as they do not doubt that they can speak. There are five physical sensations of perception: sight, hearing, tasting, feeling and smelling. Here 'speaking' has been singled out probably because the faculty of speech is the only one where there can be no trace of deception or illusion, whereas the other sensations, on account of ailments, can get contorted. Differences in hearing and seeing are known. In sickness the sensation of tasting gets reversed or distorted in some other way. Sometimes sweet things taste bitter and bitter things taste sweet. (Qurtubi)