Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) narrated: The Prophet (peace and blessings be upon him) passed by two men who were tied together and on their way to Hajj; they had made a vow. The Prophet (peace and blessings be upon him) said: "Both of you, remove your rope." They said: "O Messenger of Allah! It is a vow." The Prophet (peace and blessings be upon him) said: "Both of you, remove your rope, and then go for Hajj."
Imam al-Tabarani recorded it in al-Mu'jam al-Awsat; its chain contains a narrator, Muhammad bin Kurayb, who is da'if (weak).