The ruling on relying on astronomical calculations for the start of the month

The questioner:
The Shaykh’s case: If the believer announces at the door, I accept, and we do not have a meal, and that is according to the width of the door, because he holds onto it and takes it, so upon sleep he endures it, or upon the trials that he shares with his door in those two verses.

The Shaykh:
It is not permissible to act based on calculations, and the one who issues a fatwa to this effect has an incorrect fatwa, and his fatwa is not relied upon. Rather, one relies on the sighting, so you fast with those who based their fasting on the sighting; you fast with them. It is not permissible to rely on calculations, because Allah did not make it a sign. The Prophet (peace and blessings be upon him), as mentioned earlier in the beginning of the book, says: So complete the count of Sha'ban as thirty days. This is what the Messenger (peace and blessings be upon him) commanded us to do, and he did not refer us to calculations. Yes.