1 Corinthians 14:21

It is written in the Law: “By strange tongues and foreign lips I will speak to this people, but even then they will not listen to Me, says the Lord.”

Note Isaiah 28:11–12

BSB · Berean Standard Bible
In the law it is written, With men of other tongues and other lips will I speak unto this people; and yet for all that will they not hear me, saith the Lord.
KJV · King James Version
In the law it is written, “By men of strange languages and by the lips of strangers I will speak to this people. They won’t even listen to me that way, says the Lord.”
WEB · World English Bible
In the law it is written, By men of strange tongues and by the lips of strangers will I speak unto this people; and not even thus will they hear me, saith the Lord.
ASV · American Standard Version

Related passages

From the Treasury of Scripture Knowledge, grouped by the word they explain.

the law
The passage quoted is taken from the prophet Isaiah; but the term torah, Law, was used by the Jews to express the whole Scriptures, law, prophets, and hagiographia; and they used it to distinguish these Sacred Writings from the words of the scribes. It is not taken from the LXX., from which it varies as much as any words can differ from others where the general meaning is similar. It accords much more with the Hebrew; and may be considered as a translation from it; "only what is said of God in the third person, in the Hebrew, is here expressed in the first person, with the addition of [lego kurios ,"] saith the Lord.--Dr. Randolph.
John 10:34; Romans 3:19
With
Deuteronomy 28:49; Isaiah 28:11, 12; Jeremiah 5:15