Muwatta Malik 1824
موطأ مالك#1824SahihMalik 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
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Salim al-HilaliSahih
In-book reference: 56:14