Allah Almighty says: {Secret talks are only prompted by Satan} [Surat al-Mujādalah: 10]
1598/1- Ibn ‘Umar (may Allah be pleased with him and his father) reported that the Messenger of Allah (may Allah’s peace and blessings be upon him) said: “When there are three persons, two of them should not engage in private conversation excluding the third.” [Narrated by Al-Bukhāri and Muslim]
It was also narrated by Abu Dāwūd who added: “Abu Sālih said: ‘I asked Ibn ‘Umar: What if they are four?’ He said: ‘There is nothing wrong if you do that then.’”
The Hadīth was also narrated by Mālik in Al-Muwatta’ on the authority of ‘Abdullah ibn Dinār who said: “Ibn ‘Umar and I were at the house of Khalid ibn ‘Uqbah that was in the marketplace. A man came and wanted to talk to him (Ibn ‘Umar) in private while there was no one with Ibn ‘Umar but me. So Ibn ‘Umar called for another man to make us four. Then, he said to me and the third man that he called: ‘Move back a little, for I heard the Messenger of Allah (may Allah’s peace and blessings be upon him) say: “Two people should not hold a secret conversation excluding a third.”’”
1599/2- Ibn Mas‘ūd (may Allah be pleased with him) reported that Allah’s Messenger (may Allah’s peace and blessings be upon him) said: “If you are three, then two should not converse privately to the exclusion of the third until more people join you, because that would grieve him.” [Narrated by Al-Bukhāri and Muslim]
1) It is forbidden for two persons to engage in private conversation while excluding the third because this harms the believers. The same applies when three persons do that to the exclusion of the fourth, or four to the exclusion of the fifth and so on, if the left out person is saddened by this.
2) It is permissible to engage in private conversation when there is an assembly of people.
The Hadīth manifests the comprehensiveness of Islam as it addresses all the aspects of life with its directives, instructions, and etiquettes. There is nothing, big or small, in the life of mankind except that Islam has explained and clarified it. So, we Muslims should rejoice in complying with the laws of our great religion.