Where in the Hebrew Bible does it talk about selfishness?

Answer 1

"The acts of the sinful nature are obvious: sexual immorality, impurity and debauchery; idolatry and witchcraft; hatred, discord, jealousy, fits of rage, selfish ambition, dissensions, factions and envy; drunkenness, orgies, and the like. I warn you, as I did before, that those who live like this will not inherit the kingdom of God." - Galatians 5:19-21

Answer 2

Selfishness is not a very common idea in the Hebrew Bible. There are only two passing references to it in Psalms and Proverbs:

Psalms 119:36 Turn my heart toward your statutes, not toward selfish gain.

Proverbs 18:1 An unfriendly man pursues selfishness, and defies all sound judgment.