Critical thinking is of very high importance in our information age. Knowledge of logical fallacies and their detection in discourses is one of the significant end results of it. Islamic and Western critical thinking have many common shared characteristics, yet there are some essential differences between them. These differences are because of the differing understanding and perception of ontology, epistemology, and ethics. This research paper explains the Western stand of critical thinking on Argumentum ad Hominem (Argument Directed at the Person) and then provides its critical evaluation from Islamic perspective. According to the Western critical thinking, knowledge cannot be rejected by attacking the personality of the person who claims it, doing so amounts to the fallacy of Argumentum ad Hominem. However, according to Islamic perspective as it has roots in the original sources of Islam and in its historical scholarly tradition there are some distinctions that are necessary to be made regarding the issue. In brief, knowledge in Islam could be divided into transmitted knowledge (al-ulum al-naqliyah) and rational knowledge (al-ulum al-aqliyah). The fallacy of Argumentum ad Hominem in Islamic tradition is irrelevant to transmitted knowledge (al- ulum al-naqliyah), when historical reports and narrations are rejected because of the unreliability and known vices of their reporter as being liars, untrustworthy, having a sectarian bias, dishonest, etc. The fallacy of Argumentum ad Hominem is relevant to rational knowledge.