The stronger view is that the beginning of Ramadan may be established by the testimony of one upright, trustworthy Muslim man when the competent authority verifies his testimony. Abdullah ibn Umar, may Allah be pleased with them both, said:

Reported by Abu Dawud (2342). Scholars have used it as evidence for accepting one person's testimony to establish the beginning of Ramadan.

An upright witness here means someone known for truthfulness, trustworthiness, and religious integrity, whose sighting is possible and who accurately identifies what he saw. The observer does not issue a ruling for the public on his own; he informs the competent authority so that it can verify his testimony and announce the ruling.

To establish the end of Ramadan and the beginning of Shawwal, however, the majority of scholars require the testimony of two upright men. They do not regard one person's testimony as sufficient in this case, unlike the beginning of Ramadan.

If sighting the crescent is not established on the night preceding the thirtieth day of Sha'ban, Muslims complete thirty days of Sha'ban. This applies whether the sky is clear but the crescent is not seen, or clouds, dust, or something else prevent its sighting. The following day is then the first of Ramadan.

Aishah, may Allah be pleased with her, said:

Reported by Abu Dawud (2325), and graded authentic by al-Albani.

Clouds therefore do not shift the ruling to calculation, nor make the following day part of Ramadan merely as a precaution. The Sunnah is to complete thirty days of Sha'ban.

It is not permissible to rely on astronomical calculation to establish the beginning or end of Ramadan. The Prophet, peace and blessings be upon him, linked the ruling to sighting the crescent. If the sighting was not established, he instructed people to complete thirty days; he did not make calculation an alternative.

Abdullah ibn Umar, may Allah be pleased with them both, reported that the Prophet, peace and blessings be upon him, said:

Reported by al-Bukhari (1913) and Muslim. Al-Bukhari's narration explains that this means sometimes twenty-nine days and sometimes thirty. A lunar month therefore has neither more than thirty days nor fewer than twenty-nine.

The hadith does not criticize writing or beneficial knowledge. Rather, it explains that the ruling on the month's beginning is tied to a clear, generally accessible sign, not dependent on the knowledge of a group of calculators. The guidance of the Prophet, peace and blessings be upon him, and his Companions was therefore to look for the crescent and then complete the prescribed number of days if a sighting was not established.

Worship is based on following revealed guidance. The precision of calculations concerning conjunction or the positions of celestial bodies does not change the prescribed basis on which fasting begins and ends. Shaykh Abdul Aziz ibn Baz, may Allah have mercy on him, affirmed acting upon a sighting, even through an optical aid, rather than calculation alone.

The moon's birth, or astronomical conjunction, is an astronomical event whose time can be calculated. It may occur before sunset without the crescent being visible afterward. Sighting means actually observing the crescent, not calculating the time of conjunction or predicting its possible appearance. Crescent visibility is affected by the observer's location, weather conditions, and the crescent's proximity to the sun. Conjunction having occurred therefore does not mean the crescent has been seen.

It is consequently not enough for a calendar to state that the moon has been born, that the astronomical month has begun, or that the probability of visibility is high. Establishing the beginning of Ramadan is a religious ruling based on a valid sighting or completing thirty days of Sha'ban.

An optical aid or optical observatory may be used to help sight the crescent. This strengthens eyesight and achieves the sighting itself; it does not establish the month by calculation alone. If a trustworthy observer sees the crescent through an acceptable optical means and the competent authority accepts the testimony, the sighting is acted upon.

Tables, software, and predictive images describing the moon's birth or possible visibility do not themselves replace testimony to an actual sighting, and Ramadan does not begin merely because they are published. A circulating image is also insufficient to establish the month unless the competent authority verifies its source, the validity of the sighting, and the acceptance of the testimony. An image appearing on a screen is not, in itself, a religious announcement that the month has begun.

Scholars differed about varying lunar horizons: does a sighting in one country bind all Muslims, or does each country or region have its own sighting when locations are far apart and their horizons differ? This is a longstanding, recognized disagreement in Islamic jurisprudence.

Among the strongest evidences cited by those who take differing horizons into account is the hadith of Kurayb, who reported:

Reported by Muslim (1087).

Ordinary Muslims should not turn this disagreement into conflict within a family or mosque, nor should each person choose the country that suits their preference. The competent Islamic authority adopts the scholarly position it considers stronger, and Muslims in its country follow it.

Differences may occur for recognized reasons, including differing horizons, testimony being established in one country but not another, or differences between authorities in accepting and verifying reports. Not every difference is evidence of manipulation or error.

However, if an announcement is based on calculation alone, without a sighting or completion of the prescribed number of days, this is not the prescribed Islamic method of establishing the month.

Applications and calendars are useful for anticipated dates and preparation, but they do not establish Ramadan's beginning by themselves. An application marking a particular date is therefore insufficient to rule that it is the first of Ramadan. Reliance is placed on an announcement based on an established, valid sighting or completing thirty days of Sha'ban.

Likewise, circulating images and posts are not relied upon until their source is known and the competent authority confirms the validity of the sighting.