Nations Who Denied Their Prophets Will Be Questioned
These nations will deny that their prophets delivered them Allah's message, so the Muslims will testify to the truth based on what they have been told in the Quran that these prophets did do so.
"It is He Who has named you Muslims both before and in this (Revelation); that the Apostle may be a witness for you and you be witnesses for mankind!"
(Quran: 22;78)