Surah 33. Al-Ahzab, Ayah 36

I.e., whenever a specific law has been formulated as such in the Qur'an or in an injunction promulgated by the Prophet.

Lit., "to have a choice in their concern (min amrihim)" - i.e., to let their attitude or course of action be determined, not by the relevant law, but by their personal interests or predilections.

 Meaning, if Allah makes a ruling in the Quran or the Prophet (ﷺ) makes a ruling, then a Muslim is not allowed to seek judgment from anyone else, nor follow their own desires.

We must not put our own wisdom in competition with Allah's wisdom. Allah's decree is often known to us by the logic of facts. We must accept it loyally, and do the best we can to help in our own way to carry it out. We must make our will consonant to the Allah's Will.