Exodus 31:16
"Wherefore the children of Israel shall keep the sabbath, to observe the sabbath throughout their generations, for a perpetual covenant."
Cross References (ranked by relevance)
Jeremiah 50:5
They shall ask the way to Zion with their faces thitherward, saying, Come, and let us join ourselves to the LORD in a perpetual covenant that shall not be forgotten.
Genesis 17:11
And ye shall circumcise the flesh of your foreskin; and it shall be a token of the covenant betwixt me and you.
Genesis 9:13
I do set my bow in the cloud, and it shall be for a token of a covenant between me and the earth.