Narrated 'Aisha (the mother of the faithful believers, may Allah be pleased with her):

Al-Harith bin Hisham asked Allah's Apostle "O Allah's Apostle! How is the Divine Inspiration revealed to you?" Allah's Apostle replied, "Sometimes it is (revealed) like the ringing of a bell, this form of Inspiration is the hardest of all and then this state passes off after I have grasped what is inspired. Sometimes the Angel comes in the form of a man and talks to me and I grasp whatever he says."

'Aisha added: Verily I saw the Prophet being inspired Divinely on a very cold day and noticed the Sweat dropping from his forehead (as the Inspiration was over).

حَدَّثَنَا عَبْدُ اللَّهِ بْنُ يُوسُفَ، قَالَ أَخْبَرَنَا مَالِكٌ، عَنْ هِشَامِ بْنِ عُرْوَةَ، عَنْ أَبِيهِ، عَنْ عَائِشَةَ أُمِّ الْمُؤْمِنِينَ ـ رضى الله عنها ـ أَنَّ الْحَارِثَ بْنَ هِشَامٍ ـ رضى الله عنه ـ سَأَلَ رَسُولَ اللَّهِ ﷺ فَقَالَ يَا رَسُولَ اللَّهِ كَيْفَ يَأْتِيكَ الْوَحْىُ فَقَالَ رَسُولُ اللَّهِ ﷺ " أَحْيَانًا يَأْتِينِي مِثْلَ صَلْصَلَةِ الْجَرَسِ ـ وَهُوَ أَشَدُّهُ عَلَىَّ ـ فَيُفْصَمُ عَنِّي وَقَدْ وَعَيْتُ عَنْهُ مَا قَالَ، وَأَحْيَانًا يَتَمَثَّلُ لِيَ الْمَلَكُ رَجُلاً فَيُكَلِّمُنِي فَأَعِي مَا يَقُولُ ". قَالَتْ عَائِشَةُ رضى الله عنها وَلَقَدْ رَأَيْتُهُ يَنْزِلُ عَلَيْهِ الْوَحْىُ فِي الْيَوْمِ الشَّدِيدِ الْبَرْدِ، فَيَفْصِمُ عَنْهُ وَإِنَّ جَبِينَهُ لَيَتَفَصَّدُ عَرَقًا.