It is narrated from Sayyiduna Zayd bin Thabit (may Allah be pleased with him) that he said: "I used to write down the revelation for the Messenger of Allah (peace and blessings be upon him), and his (peace and blessings be upon him) state was such that when revelation came down upon him, an intense heat would overcome him and he would sweat profusely, like pearls; then that state would be lifted from him (peace and blessings be upon him). So I would come to him (peace and blessings be upon him) with a piece of shoulder bone or some other fragment, and I would write while he (peace and blessings be upon him) dictated to me. I would not finish writing before I felt, because of the weight of the Qur'an, as if my leg were about to break, so much so that I would say (to myself) that I would never again be able to walk on this leg of mine. Then, when I had finished, he (peace and blessings be upon him) would say: 'Read it out,' so I would read it; and if anything had been left out of it, he (peace and blessings be upon him) would correct it, and then I would take it out to the people."
Hadith Referenceالمعجم الأوسط / باب الألف / 1913
Hadith Takhrij«أخرجه الطبراني فى «الكبير» برقم: 4787، 4888، 4889، والطبراني فى «الأوسط» برقم: 5880»