Abu khaythama narrated to us, (saying): Jareer related to us from Mansoor from Abu Ad-Duhaa from Masrooq, (who) said: Once we were sitting with Abdullaah (Ibn Mas’ood) whilst he was reclining; then a man came to him and said: O Abu Abdir-Rahmaan! Verily there is a story teller at the doors of Kinda claiming that the portent of the Smoke will come along and snatch the breaths of the disbelievers (i.e. take their souls away) and the believers will get something like a cold from it. So Abdullaah said while sitting up and he was angry, ”O people fear Allaah! Whoever amongst you has knowledge of something, then he should speak with what he knows; and whoever does not know, then he should say, ‘Allaah knows best’. That is because it the best of knowledge for one of you to say, ‘Allaah knows best’ with regards to things he has no knowledge of. Indeed, Allaah (The Most High) said to His Prophet (alayhis-salaam): [قُلۡ مَآ أَسۡـَٔلُكُمۡ عَلَيۡهِ مِنۡ أَجۡرٍ۬ وَمَآ أَنَا۟ مِنَ ٱلۡمُتَكَلِّفِينَ   -‘ Say (O Muhammad): No wage do I ask of you for this (the Qur’aan), not am I one of the Mutakallifun (those who pretend and fabricate things which do not exist)].” [38:86]


Source: Kitaabul Ilm of Abu Khaythama with the checking of Imaam Al Albaanee, page19. Narration number 67]