Is a Companion's opinion a legal proof?

One of the questions of legal theory on which Ibn Qayyim al-Jawziyya writes at length in I'lam al-Muwaqqi'in is whether a Companion's opinion is a proof. He gives many arguments that following the Companions is obligatory, and reports the view of those who do not hold it to be a proof. ^{1 2}

His twenty-fourth argument is the report of Hudhayfa, narrated by al-Tirmidhi, about following Abu Bakr and Umar. ¹ He states that the Companions' interpretation of the Qur'an comes before every other in all kinds of interpretation. They knew the Arabs' language best, he says, witnessed the revelation and knew its circumstances. ³ He explains that those who hold a Companion's opinion to be a proof order the proofs as the Qur'an, then the Sunna, then the Companion's opinion, then analogy. For them a Companion's opinion is stronger than an analogy that contradicts it. ^{2 4}

He discusses whether a Successor's opinion is a proof when no Companion or Successor contradicts it. His answer is that the Successors were spread so widely that one can hardly be confident no one disagreed. He notes that some Hanbalis and Shafi'is held that such an opinion should be followed, and that al-Shafi'i said in one place that he held a view in deference to Ata. Most scholars, he adds, distinguish between Companion and Successor, and two narrations are reported from Ahmad on using a Successor's interpretation as proof. ³

Ibn al-Qayyim reports that those who say a Companion's opinion is not a proof hold two views when it goes against analogy. One is that it is all the more not a proof, since it contradicts a legal proof. The other is that in that case it is a proof, on the assumption that the Companion said it on the basis of something he learned from the Prophet ﷺ, so that it is like a mursal report acted on by the one who narrated it. ²

The holders of the view that it is not a proof have not yet been added by name, with their arguments from the books of legal theory. Ibn al-Qayyim's earlier arguments, in the preceding volume, have not been added either.