Promise of Loyalty is a rare Sorcery card from Secrets of Strixhaven Commander (SOC), collector number 161. Current market price: $0.31, TCGplayer market prices via Scryfall.
Each player puts a vow counter on a creature they control and sacrifices the rest. Each of those creatures can't attack you or planeswalkers you control for as long as it has a vow counter on it.