Shaykh al-Islām Ibn Taymiyyah [d. 728 AH] said:

The [Christians’] usage of even a single word of the Prophet Muḥammad (ﷺ) to support [their religion] is completely invalid; incorrect in every conceivable way.

For, indeed, if he [the Prophet [ﷺ]] was a truthful messenger [of God] it would have been incumbent on him to relate the truth from Allāh the Exalted in Might in everything [which he has related].

Every individual is well aware that he brought that which is contrary to the Christian religion. Therefore, it would stand to reason that if he was a truthful messenger, then the Christian religion must be false. Otherwise, if they [the Christians] should ever claim that a single word of his [the Prophet [ﷺ]] as being false, then according to them he could not be counted as a truthful messenger of Allāh. Therefore, whatever they [the Christians] claim regarding him whether it be that he was a just ruler, or a scholar from among the scholars, or a pious man from among the pious, or a saint from among the saints and however they glorify or praise him in the face of what is apparent to them from his extraordinary characteristics of goodness and evident distinctions, and his pure legislations; should they disbelieve in even a single word of what he brought, or have a doubt concerning it, then they have disbelieved in him regarding his claim that he is a messenger of Allāh, and that he has delivered this Qurʾān from Him. Whomsoever should claim falsely that he is a messenger of Allāh could not be from among His prophets or messengers. Thus, whoever is not from among them, his postulations could never be considered as evidence, rather his [words] should be held with the same regard as anyone else.

Source: Al-Jawāb al-Ṣaḥīḥ 1:143
Translated by: Riyāḍ al-Kanadī