Jami` at-Tirmidhi 3632

Narrated 'Aishah:"The first of what the Messenger of Allah (ﷺ) initiated with of Prophethood, when Allah wanted to honor him and grant His mercy upon His creatures, was that he would not see anything (in a dream) except that it would occur like the break of dawn. So he continued upon that for as long as Allah willed for him to continue, and seclusion was made beloved to him, such that there was not anything more beloved to him than being alone