Malik bin Anas narrated, from Ibn Shihab, from Muhammad bin "Abdullah bin al-Harith bin Nawfal bin Abdul Muttalib, that he told him that

He heard Sa"d bin Abi Waqqas and ad-Dahhak bin Qais, the year Mu"awiyah bin Abi Sufyan performed Hajj and they were talking about continuing umrah on to the Hajj (tamattu" or qiran), Ad-Dahhak said: “No one does that except one who is ignorant of the command of Allah.” Sa"d said: “What a bad thing you have said, O son of my brother!” Ad-Dahhak said: "Umar bin al-Khattab has forbidden that,” Sa"d said: “The Messenger of Allah (ﷺ) did it and we did it with him.”