Hadith #332
English (English)O People! He who knows something, let him say it; and he who does not know should say: Allah knows best; for it is a sign of knowledge that a person who does not know something, say: Allah knows best.
Reference: صحیح البخاري، کتاب التفسیر، باب قوله: وما أنا من المتكلفين، الحدیث 4809