Speaker John Bercow has warned MPs about making accusations in the House of Commons, after the Prime Minister was forced to apologise for claiming an imam was an Islamic State supporter.
David Cameron apologised in writing on Thursday for accusing Sulaiman Ghani of supporting IS during Prime Minister's Questions last month.
Former Tory leadership rival David Davis complained during a point of order in the Commons that the Prime Minister's written apology did not have the "same prominence as the original allegation".
Speaker John Bercow said: "What a Member says in this place is the responsibility of that Member.
"While parliamentary privilege is an essential protection of free speech, all Members should reflect carefully before criticising individuals."
Referring to the author of a book on parliamentary practice, he added: "As Erskine May notes, it is the duty of each Member to refrain from any course of action prejudicial to the privilege he enjoys.
"It is not for the chair to require a Member to apologise on the floor of the House but it is perfectly open to a Member to do so.
"Good grace and magnanimity in these circumstances I know are always appreciated."
Mr Cameron first issued an apology through a Downing Street spokeswoman before using a parliamentary device to retract the comment in writing, to avoid taking to the despatch box.