It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) did not disclose the matter of (digging) the trench to anyone except six men: four of the Muhajirun: Talhah, al-Zubayr, Ali and Sa'd; and of the Ansar: Abu Dujanah and al-Harith bin al-Simmah.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 13353