قد روي عن أبي حنيفة أنه قال: لا خمس في العنبر
It is reported from Abu Hanifah that no khums is due on ambergris.
Ambergris is associated with the sea. The legal question is whether the rule of spoils, minerals, or some other category governs the levy. To decide the inference one must identify the legal cause relevant to khums in the proposed comparison.
Merely saying that “ambergris is like fish” is insufficient unless a legally relevant shared cause is established for the particular rule at issue.