Celebrate special days such as religious holidays or days when important revelations were made.

This hadith is about how Umar bin Al-Khattab responded to a Jew who said that if they were the ones to whom an ayat was revealed, they would have taken that day as a day of celebration. The ayat in question is from Surat al Ma'idah and it reads "This day, I have perfected your religion for you, completed My favor upon you, and have chosen for you Islam as your religion". Umar then informed him that this ayat was revealed on the Day of 'Arafah which falls on Friday. This hadith teaches us about celebrating special days such as religious holidays or days when important revelations were made. It also shows us how knowledgeable and wise Umar was in his understanding of Islamic teachings.