Our Prophet (saas) has seen Hazrat Mahdi (pbuh) when he was in a state between sleep and awareness

103- Ghaibat Nomani: It is narrated from Ibne Uqdah from Ahmad bin Yusuf from Ismail bin Mahran from Ibne Bataini from Wuhaib from Abu Basir from Imam Muhammad Baqir (a.s.) that he said:  By Allah, as if I see him (the Qaim) between the corner (of the Kaaba) and the Place of Ibrahim. 

(The Promised Mahdi, Allamah Muhammad Baqir Al-Majlisi, English Translation of Biharul Anwar, Volume 13 (Old Edition)/ Volum 51-52-53 (New Edition), Kitabul Gaibah-Book of Occultation, Imam Mahdi(a.t.f.s)- The Twelfth Imam of the Twelver Shia, Part II, Translator; Sayyid Athar Husain S.H. Rivzi)