Yusuf bin Mazin al-Rasibi (may Allah have mercy on him) said: A man stood up before Sayyiduna al-Hasan bin Ali (may Allah be pleased with him) and said: You have blackened the faces of the believers. He said: "Do not reproach me, may Allah have mercy on you, for the Messenger of Allah (peace and blessings be upon him) was shown the Banu Umayyah delivering sermons on his pulpit one after another, and that grieved him (peace and blessings be upon him). So this verse was revealed: 'Indeed, We have given you al-Kawthar' [Surah al-Kawthar: 1], that is, a river in Paradise. And this was revealed: 'Indeed, We sent it down on the Night of Decree. And what will make you know what the Night of Decree is? The Night of Decree is better than a thousand months' [Surah al-Qadr: 1-3], (months which) the Banu Umayyah will rule." Al-Qasim said: "We calculated that, and it came to a thousand (months), neither more nor less."
Hadith Referenceالمعجم الكبير للطبراني / باب الحاء / 2741