It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that a man came to Madinah, so the Messenger of Allah (peace and blessings be upon him) said to him: "No man should sit in seclusion with a woman except that her mahram relative is with her."
Hadith Referenceمسند اسحاق بن راهويه / كتاب المناسك / 320
Hadith Takhrij«طبراني كبير : 121/12 . مصنف عبدالرزاق ، رقم : 10750 . حديث صحيح»