The correct expression is "By mutual agreement"From a legal point of view, the "common agreement" to sign a contract, commitment, is reached when there is a unanimous opinion towards the terms of the out-of-court or judicial agreement. It is ALWAYS a unanimous agreement of the parties signing it. From a religious point of view, "Common Accord" refers to a prayer directed by the holy spirit, which indicates how to pray focusing on God or not on the opinion of others. Informally refers to a decision taken or an action executed, by 2 or more persons, without sole responsibility of one of them.