What is the ruling on the fast of one who ate and drank after the dawn (Fajr) adhan, based on the fatwa of a shaykh who believes the adhan time is incorrect?

The obligation in fasting is to abstain from nullifiers from the rise of dawn until sunset. If a Muslim is certain of the rise of dawn, he must abstain. However, if he doubts whether the time of the muezzin's call to prayer is before or after dawn, it is preferable to abstain immediately upon hearing the adhan as a precaution. But there is no harm in eating and drinking if one is not certain of the rise of dawn. And if one emulates someone trustworthy who states that the adhan precedes the true dawn, there is no harm upon him, and his fast is valid. The safer approach for fasting is to abstain with the adhan, and for prayer, to delay it by twenty minutes or more.