Tafsir of Al-Hajj 22:68

And if they argue with you, say: "Allah knows best what you do.'' This is like the Ayah:

وإن كذبوك فقل لى عملى ولكم عملكم أنتم برييون مما أعمل وأنا برء مما تعملون

And if they belie you, say: "For me are my deeds and for you are your deeds! You are innocent of what I do, and I am innocent of what you do!'' (10:41)

الله أعلم بما تعملون

Allah knows best of what you do. This is a stern warning and definite threat, as in the Ayah:

هو أعلم بما تفيضون فيه كفى به شهيدا بينى وبينكم

He knows best of what you say among yourselves concerning it! Sufficient is He as a witness between me and you! (46: 8) Allah says here:

الله يحكم بينكم يوم القيامة فيما كنتم فيه تختلفون