BT Ket 70a(31) :כיון דמשעבדה ליה לאו כל כמינה דמפקע שיעבודיה‏ : since she is obligated to him it is not up to her to cancel her obligation
See the entire entry for šiˁbūḏ, šiˁbūḏā v.n.Q enslavement, servitude