Shaikhul Islaam Ibn Taymiyyah (rahimahullaah) stated:
Regarding distinction between truth and falsehood; guidance and misguidance; the path leading to guidance and the path leading to misguidance; the path of happiness (in this life and the next) and the path of wretchedness and destruction; then everything that Allaah revealed to His Messengers and in His Books is obligatory to be followed -[i.e. as it is well known from the statements of the scholars that all the Prophets and Messengers have the same creed (i.e. issues of Imaan, Tawheed etc) and everyone is obligated to follow them, but after the advent of Muhammad (sallal-laahu-alayhi-wasallam) all the issues related to the ahkaam (i.e. rulings on different affairs of worship, dealings etc) from the other Prophets and Messengers have been abrogated, and only Muhammad’s Sharee’ah is to be followed. Likewise, all the previous books have been abrogated after the revelation of the Qur’aan). See Tafseer Surah Al-Maa’idah regarding this affair Aayaat 48-50]- and through it one acquires distinction between right and wrong, guidance, knowledge and Eemaan.
Allaah (The Most High) testified that it (i.e. His Revelation) is the truth and a testimony to the truth, and what is in opposition to it from the statements of the people are displayed before it for inspection- if (a statement) is in agreement with it, then it is truth, and if in opposition, it is falsehood.
(But), if it is unknown whether (a statement) is in opposition or in agreement due to its general nature, or the meaning intended by the utterer is known or unknown, but it is unknown whether the Messenger (sallal-laahu-alayhi-wasallam) has brought something that testifies to (its correctness) or declares it to be false, then one abstains and does not speak except with knowledge, for knowledge is that which is established with evidence and what is beneficial of it is that which the Messenger came with. The Messenger (sallal-laahu-alayhi-wasallam) is the most knowledgeable amongst the creation and he has the greatest desire in acquainting the creation with it. He is the most capable in giving a clarification and definition of it. He is above everyone in knowledge, ability and intent, and through these three affairs the goal is accomplished. (However), those besides the Messenger (sallal-laahu-alayhi-wasallam) are either deficient or corrupted in their knowledge.
[Source: Majmoo Ar-Rasaa-il Al-Kubraa (1/102)]