It is not permissible to rely on calculation in fasting

Question: In some Muslim countries, people resort to fasting without relying on the sighting of the crescent moon, and they are content with the calendars. What is the ruling on that?


Answer: The Prophet (peace and blessings be upon him) ordered the Muslims to fast upon seeing it, and if it was obscured from them, to complete the count of thirty. This is agreed upon by al-Bukhari and Muslim. He (peace and blessings be upon him) also said: and he hid his thumb on the third occasion and said: and he gestured with all his fingers. By this, he meant that the month can be twenty-nine days and it can be thirty days.
And it is established in Sahih al-Bukhari from Abu Hurayrah (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: .
And he (peace and blessings be upon him) said: . The hadiths in this chapter are numerous, and all of them indicate the obligation to act upon the sighting, or to complete the count in the absence of the sighting. They also indicate that it is not permissible to rely on calculation in this matter. Shaykh al-Islam Ibn Taymiyyah (may Allah have mercy on him) reported the consensus of the scholars that it is not permissible to rely on calculation in establishing the new moons. End of quote. And this is the truth in which there is no doubt. And success is from Allah.