The Holy Qur’an is held sacred by all Muslims. The noble Sahabah (may Allah be pleased with them) were keen to learn everything having to do with it, such as the reasons for revelation, the story behind the revelation of verses, and when they were revealed, as well as learning all the rulings and meanings of the verses. In this report, the Tabi‘i Tariq ibn Shihab narrates that a Jewish man – namely Ka‘b al-Ahbar, before he became Muslim, as is narrated in Tafsir al-Tabari and al-Awsat by al-Tabarani – came to the caliph ‘Umar (may Allah be pleased with him) and said to ‘Umar (may Allah be pleased with him): There is a verse in your Book that you recite; if it had been revealed to us Jews, we would have taken that day as a festival – that is, we would have made it a festival to celebrate, out of respect and honour for that day, and highlighting its virtue. ‘Umar said: Which verse is it? He said: {This day I have perfected for you your religion} [al-Ma’idah 5:3], that is, by causing it to be victorious and prevail over all other religions, {and completed My favor upon you} that is, by guiding you, helping you and perfecting the religion, and with the conquest of Makkah and the destruction of the beacons of jahiliyyah. This is a great verse, and the day when it was revealed is deserving of celebration. ‘Umar (may Allah be pleased with him) said: We know that day, and the place in which this verse was revealed, so you are not telling us of something of which we are unaware. It was revealed to the Prophet (blessings and peace of Allah be upon him) when he was standing in ‘Arafah on a Friday, so it was a day on which two “festivals” were combined: the day of ‘Arafah, and Friday. The words of Ka‘b al-Ahbar, “we would have taken that day as a festival” imply: and you have not taken it as a festival, as if he was trying to suggest that the verse was not true, because the Muslims had neglected the day on which it was revealed. So ‘Umar explained to him that they did indeed celebrate it on two counts, and they regarded it as a twofold festival. This hadith indicates that festivals and days to be commemorated cannot be based on personal opinion and ideas, as the People of the Book (Jews and Christians) did before us. Rather they are to be based on religious texts and following the practice of the Prophet (blessings and peace of Allah be upon him). It also indicates that faith may increase and decrease, as religious commitment may be perfected by perfecting and completing the deeds that it prescribes..