Sayyiduna Abdullah bin Salam (may Allah be pleased with him) was sitting, and he said something which a man overheard, although he did not like that man to hear it. So he turned to Sayyiduna Abu al-Darda' (may Allah be pleased with him) and said: I heard the Messenger of Allah (peace and blessings be upon him) saying: "Whoever narrates something and does not want it to be disclosed, it is a trust, even if the one who narrated it did not ask his companion to keep it secret."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 14001