they said take a mutual oath by allah that we will kill him by night he and his family. then we will say to his executor we did not witness the destruction of his family and indeed we are truthful. 
قالوا تقاسموا بالله لنبيتنه وأهله ثم لنقولن لوليه ما شهدنا مهلك أهله وإنا لصادقون