Sunan An-Nasai, Chapter: The Book of Leading the Prayer (Al-Imamah)

"While I was in the Masjid in the first row, a man pulled me from behind and moved me aside, and took my place. By Allah, I could not focus on my prayer, then when he left I saw that it was Ubayy bin Kab. He said: 'O boy, may Allah protect you from harm. This is what the Prophet (saw) instructed us to do, to stand directly behind him.' Then he (Ubayy) turned to face the Qiblah and said: 'Doomed are Ahl Al-Uqd, by the Lord of the Kabah! - three times.' Then he said: 'By Allah, I am not sad for them, but I am sad for the people whom they have misled.' I said: 'O Abu Yaqub, what do you mean by Al Al-Uqd?' He said: 'The rulers.'" (Sahih)