Psalm 151 is recognized as Deuterocanonical Scripture by the Greek Orthodox and Russian Orthodox Churches.
This Psalm is a genuine one of David (though extra*) composed when he fought in single combat with Goliath.
1 I was small among my brothers,
and youngest in my father’s house.
I tended my father’s sheep.
2 My hands formed a musical instrument,
and my fingers tuned a lute.
3 Who shall tell my Lord?
The Lord himself, he himself hears.
4 He sent forth his angel and took me from my father’s sheep,
and he anointed me with his anointing oil.
5 My brothers were handsome and tall;
but the Lord didn’t take pleasure in them.
6 I went out to meet the Philistine,
and he cursed me by his idols.
7 But I drew his own sword and beheaded him,
and removed reproach from the children of Israel.
*^ or, supernumerary