Sayyiduna Sahl bin Sa'd (may Allah be pleased with him) narrates that he heard Sayyiduna Zayd bin Thabit (may Allah be pleased with him) say: "When revelation came down upon the Messenger of Allah (peace and blessings be upon him), its weight became heavy upon him (peace and blessings be upon him), and his (peace and blessings be upon him) forehead would be drenched with sweat, as if it (the sweat) were pearls."
Imam al-Tabarani (may Allah have mercy on him) said: "No one except Uthman bin Abd al-Rahman narrated this hadith from al-Zuhri, and Yunus bin Bukayr is alone in narrating it."
Hadith Referenceالمعجم الأوسط / باب الميم / 5880
Hadith Takhrij«أخرجه الطبراني فى «الكبير» برقم: 4787، 4888، 4889، والطبراني فى «الأوسط» برقم: 1913»