Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) says: Beware of bearing witness (that someone is a martyr)! If you must do so, then bear witness in favour of that expedition whose members the Messenger of Allah (peace and blessings be upon him) had sent out and who were then granted martyrdom. The Qur'an was revealed concerning them: "(They said:) Convey this message from us to our people: that we have come into the presence of our Lord; He is pleased with us, and He has made us pleased."
Al-Tabarani recorded it. Its chain contains Ata' bin al-Sa'ib, who had become confused (in his memory).