1 John 2:5

But whoso keepeth his word, in him verily is the love of God perfected: hereby know we that we are in him.
— 1 John 2:5, King James Version

In other translations

World English Bible (WEB)

But whoever keeps his word, God's love has most assuredly been perfected in him. This is how we know that we are in him:

American Standard Version (ASV)

but whoso keepeth his word, in him verily hath the love of God been perfected. Hereby we know that we are in him:

Young's Literal Translation (YLT)

and whoever may keep his word, truly in him the love of God hath been perfected; in this we know that in him we are.