A mursal hadith is one in which a narrator from the generation after the Companions, known as a Tabi'i, reports directly that 'the Prophet said such-and-such,' without mentioning which Companion he heard it from. Since the Tabi'un did not personally meet the Prophet, this leaves a missing link in the chain: we don't know who stood between the Tabi'i and the Prophet, and that unnamed person's reliability can't be checked. Because a fundamental requirement of a sound isnad is that every link be identified and vetted, most hadith scholars, including Imam Muslim in his introduction, treat mursal reports as a form of weak (da'if) hadith rather than fully authentic ones. There are some exceptions: a minority of scholars, including some in the Maliki and Hanafi traditions, give more weight to mursal narrations from especially rigorous early Tabi'un, particularly when the same report reaches them through other independent chains that support it. Even then, a mursal report is rarely relied upon in isolation to establish an obligatory ruling; it is usually treated as supporting evidence alongside stronger, fully connected hadith.
Q&A · Hadith
What is a mursal hadith?
References
Informational, not a personal fatwa. Consult a qualified scholar for rulings on your situation.