Is it obligatory to believe the words of a Companion that are not from the words of Allah or His Messenger, such as the hadith describing the Messenger (peace and blessings be upon him) in the Torah, and what is the ruling on one who does not believe this hadith?

The example mentioned includes the Companion's report about the existence of one of the Prophet's attributes, peace and blessings be upon him, in the Torah. This report is accepted because we are certain of the acceptance of what the Companions reported, as they are trustworthy by the consensus of the Ummah. Ibn al-Qayyim cited the verse {O you who have believed, if there comes to you a disobedient one with information, investigate} as proof that the report of a single trustworthy person is acceptable and does not require verification. And whoever rejects the Companion's report, disbelieving it without evidence, has impugned the Companions' trustworthiness, which is agreed upon among the Ahl al-Sunnah wa al-Jama'ah. As for whoever rejects the Companion's statement due to believing it lacks authority, that is another issue that has been discussed in previous fatwas.