Your thoughts guide your ally's attack so that it strikes true.

Encounter   ✦     Psionic
Immediate Interrupt      Close burst 3

Trigger: An ally within 3 squares of you makes an opportunity attack

Target: The triggering ally in the burst

Effect: The target gains a power bonus to the attack roll and the damage roll equal to your Charisma modifier.

Published in Player's Handbook 3, page(s) 34.