Which psalm begins, "He who dwells in the shelter of the Most High will abide in the shadow of the Almighty"?

Answer: Psalm 91

Psalm 91:1 (KJV: "the secret place of the most High") opens a psalm of trust: "You are my refuge and my fortress, my God."

“He who dwells in the shelter of the Most High will abide in the shadow of the Almighty. I will say to the LORD, “You are my refuge and my fortress, my God, in whom I trust.””— Psalm 91:1-2 (BSB)