Riyad as-Salihin 1629
Ibn Abbas (May Allah be pleased with them) said:
The Messenger of Allah (ﷺ) said, "No one of you should meet a woman in privacy unless she is accompanied by a Mahram (i.e., a relative within the prohibited degrees)." [Al-Bukhari and Muslim] .
وعن ابن عباس رضي الله عنهما أن رسول الله صلى الله عليه وسلم  قال‏:‏ ‏
"‏لا يخلون أحدكم بامرأة إلا مع ذي محرم‏"‏ ‏(‏‏(‏متفق عليه‏)‏‏)‏‏.‏