by Imam Malik, translation by A'isha `Abdarahman at-Tarjumana and Ya`qub Johnson , Volume: Speech
Chapter: Two People Conversing to the Exclusion of Another
Malik related to me from Abdullah ibn Dinar saying, "Abdullah ibn Umar and I were at the house of Khalid ibn Uqba who was away at the market. A man came who wanted to speak to Abdullah ibn Umar and I was the only other person present Abdullah ibn Umar called another man so that we were four and said to me and the man whom he had called, 'Go a little way off together, because I heard the Messenger of Allah, may Allah bless him and grant him peace, say, "Two do not converse secretly to the exclusion of another.' "'
Malik related to me from Nafi from Abdullah ibn Umar that the Messenger of Allah, may Allah bless him and grant him peace, said, "Two must not converse secretly to the exclusion of another person."