If a person starts telling you, whether in private or public, something that you already knew very well, pretend as if you do not know it. Do not rush to reveal your knowledge or to interfere with the speech. Instead, show your attention and concentration.

Imam Ata Bin Abi Rabah said: “A young man would tell me something that I may have heard before he was born. Nevertheless, I would listen to him as if I had never heard it before.”

Ata was a Tabi’ee, i.e. the one belonging to the generation coming after the Companions.

Khalid Bin Safwan Al-Tamimi, who frequented the courts of two Caliphs, Umar Bin Abdul Aziz and Hisham Bin Abdul Malik, said: “If a person tells you something you have heard before or news that you already learned, do not interrupt him to exhibit your knowledge to those present. This is being rude and ill-mannered.”

Ibrahim Bin Al-Junaid said: “A wise man said to his son: ‘Learn the art of listening as you learn the art of speaking.'”

Listening well means maintaining eye contact, allowing the speaker to finish the speech, and restraining your urge to interrupt his speech. Al-Hafiz Al-Khateeb Al-Baghdadi said in a poem:

Never interrupt a talk

Though you know it inside out