Harith bin Hisham asked the Messenger of Allah ﷺ, "How does the revelation come to you?"The Messenger of Allah ﷺ replied, "Sometimes it comes to me like the ringing of a bell, and that is the hardest on me. Then it leaves me, and I have grasped what was said. At other times, the angel appears to me in the form of a man and speaks to me, and I retain what he says."Ayesha said, "I saw the revelation descending upon the Messenger of Allah ﷺ on a bitterly cold day, and when it left him, his forehead was streaming with sweat."
حدثنا إسحق بن موسى الأنصاري حدثنا معن حدثنا مالك عن هشام بن عروة عن أبيه
أن الحارث بن هشام سأل رسول الله ﷺ كيف يأتيك الوحي فقال رسول الله ﷺ يأتيني في مثل صلصلة الجرس وهو أشده علي وأحيانا يتمثل لي الملك رجلا فيكلمني فأعي ما يقول قالت عائشة فلقد رأيت رسول الله ﷺ ينزل عليه الوحي في اليوم ذي البرد الشديد فيفصم عنه وإن جبينه ليتفصد عرقا
Agreed upon [by Bukhari and Muslim]. Bukhari narrated it in the Book of the Beginning of Revelation, Chapter on How the Revelation to the Messenger Began, etc., hadith no. 2, from the hadith of Malik. And Muslim, hadith no. 2333, from the hadith of Hisham on this same subject. It is also found in Muwatta, 1/202, 203.