Under which condition is a worshipper permitted to verbally respond to a Salaam (Radd al-Salaam) during the Friday sermon?

Friday Prayer Part 2: Validity and the Sermon

• If the person who greeted is a traveler.
• Only if the Imam permits it during the break.
• Under no condition, as verbal response is strictly prohibited during the sermon.
• If the Salaam is whispered.