Hebrews 6:13
For when God made a promise to Abraham, since he could swear by no one greater, he swore by himself,
World English Bible (Public Domain)
In context
Before · Hebrews 6:11–12
11We desire that each one of you may show the same diligence to the fullness of hope even to the end, 12that you won’t be sluggish, but imitators of those who through faith and perseverance inherited the promises.
13For when God made a promise to Abraham, since he could swear by no one greater, he swore by himself,