Should we follow the customs of the local people? And what is the evidence for that?

The rule "Custom is an arbitrator" (العادة محكّمة) is one of the major, agreed-upon jurisprudential maxims. The conditions for a custom to be arbitrated are that it must not contradict a fixed, authentic sacred text, and that it must be consistently followed, not irregular. A sound custom is one that people are accustomed to, does not contradict the Sharia, does not invalidate an obligation, and does not permit what is forbidden. It must be taken into consideration in legislation and judiciary because it represents the needs and interests of the people. As for a corrupt custom, it is one that contradicts the Sharia, permits what is forbidden, or invalidates an obligation, and it is not obligatory to take it into consideration. Jurists have relied on custom in many rulings, such as Imam Malik, who based rulings on the practice of the people of Medina, and Abu Hanifa, who relied on the differences in customs in some of his rulings. Examples of this include the maxim that "what is known by custom is like what is stipulated by condition," and "what is established by custom is like what is established by text."