Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) narrated: The Messenger of Allah (peace and blessings be upon him) walked with them to Baqi' al-Gharqad, then sent them off, saying: "Set off in the name of Allah. O Allah, help them." Then the Messenger of Allah (peace and blessings be upon him) returned to his house - meaning in connection with the killing of Ibn al-Ashraf.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 11505