Layali Al-Qadr (The Nights Of Destiny)

Laylat Al-Qadr is the night that the Quran was revealed to Prophet Muhammed (a.s.). The blessings you gain from the acts of worship during this night cannot be compared to any other night. This night is worth a 1,000 months (approximate 83.3334 years). The reward of acts of worship done in this one single night is more than the reward of a thousand months of worship. 

The assassination of Imam Ali (a.s) occurred in the last ten days of the Ramadan month, so we must mourn in these nights. On the 19 of Ramadan, he was hit while conducting morning prayer. He passed away two days later, on the 21st of Ramadan.