Is the ruling on knowing prayer times obligatory or recommended, and is a Muslim legally required to investigate and inquire to know when the time for prayer has begun, or is it sufficient to rely on calendars and what official bodies announce?

A Muslim must ascertain with certainty or strong probability the entry of prayer time, either by personal observation or by asking a trustworthy person.

As for calendars approved by reliable scholars, they are to be followed unless they contradict the শরীয়াহ (Islamic law) signs; otherwise, reliance on them is not permissible.

Unknown calendars should not be fully relied upon, even if they are used for approximate estimation.

Reliance on what is issued by official bodies depends on the trust one has in them.

If an error becomes apparent after following such a source, the prayer must be repeated.