The first signs of prophethood given to the Messenger of Allah ﷺ, when Allah willed to honor him and show mercy to His servants through him, was that he would not see anything except that it came to him like the breaking of dawn. He remained in this state for as long as Allah willed, and solitude was made beloved to him, so that nothing was dearer to him than to be alone.
حدثنا الأنصاري إسحق بن موسى حدثنا يونس بن بكير أخبرنا محمد بن إسحق حدثني الزهري عن عروة
أول ما ابتدي به رسول الله ﷺ من النبوة حين أراد الله كرامته ورحمة العباد به أن لا يرى شيئا إلا جاءت مثل فلق الصبح فمكث على ذلك ما شاء الله أن يمكث وحبب إليه الخلوة فلم يكن شيء أحب إليه من أن يخلو
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Agreed upon. Bukhari reported it in the Book of the Beginning of Revelation, chapter "How the Revelation to the Messenger of Allah Began... etc.," hadith no. 3, and Muslim, hadith no. 160, both from the hadith of Zuhri through this chain.