The Importance of saying Allah knows best (or Allah knows better)
Masruq (May Allah be pleased with him) said:
We visited 'Abdullah bin Mas'ud (May Allah be pleased with him) and he said to us:
O people! He who has the knowledge of any matter may convey it to the others. And he who has no knowledge, thereof, should say:
اللهُ أَعْلَم
"Allahu A'lam
(Allah knows better)."
It is a part and parcel of knowledge that a man who has no knowledge of a matter should say: "Allah knows better." Allah said to His Prophet (ﷺ):
"Say (O Muhammad (ﷺ)): 'No wage do I ask of you for this (the Qur'an), nor am I one of the Mutakallifun (those who pretend and fabricate things which do not exist)."' (38:86)
[Al-Bukhari].
Riyad as-Salihin, The Book of the Prohibited actions, Book 18, Hadith 1656 | Darussalam Translations.