Sunan an-Nasa’i 808
The Book of Leading the Prayer (Al-Imamah)
Who should stand immediately behind Imam and who should stand behind them
It was narrated that Qais bin 'Ubad said: "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 Ka'b. He said: '0 boy, may Allah protect you from harm. This is what the Prophet (ﷺ) instructed us to do, to stand directly behind him.' Then he (Ubayy) turned to face the Qiblah and said: 'Doomed are Ah1 Al-'Uqd, by the Lord of the Ka'bah! - 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: '0 Abu Ya'qub, what do you mean by Ah1 Al-'Uqd?' He said: 'The rulers."'