Ibn Mas'ud (RAA) narrated that the Messenger of Allah (ﷺ) said:
"When three of you get together in company, two of you must not talk privately while isolating the third, so as not to make him feel sad (that he is left out) till you mingle with other people (i.e. you are joined by others)." Agreed upon and the wording is from Muslim.
English reference: Book 16, Hadith 1484
Arabic reference: Book 16, Hadith 1440