Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) said: Whoever among you has knowledge should make it apparent, and whoever does not have knowledge should say about what he does not know: «لا أعلم» (that is, "I do not know"), because if a scholar is asked about something he does not know, he should say «الله أعلم» , just as Allah Almighty said to His Messenger (peace and blessings be upon him): "Say: I do not ask you for any reward for it, nor am I one of those who pretend." [سورة ص: 86/38]