It is mentioned in Advice for the Muslim, that one day, Hadrat 'Ali ® entered Masjidun Nabwi and wept long in front of Fatima's ® room. Then he entered the Hujrat as-Saada and said, "As-salamu 'alaika ya Rasul-Allah." And he wept again. Then, saying, "Alaikuma 's-salam ya akhawayya wa rahmat-Allah," he greeted Hadrat Abu Bakr ® and Hadrat 'Umar ® and went out.
[Ref: Ahmad 5:422, Al-Haakim Mustadrak 4:515; both the latter and al-Dhahabi said it was sahih. It is thus cited by as-Subki (Shifa' as-siqam p. 126), Ibn Taymiyya (al-Muntaqa 2:261f.), al Tabarani in Mu'jam al-Kabir (4:189) and Mu'jam al-Awsat according to Haythami in al-Zawa'id (5:245 and 5:441 #5845 Book of Hajj, "Section on the honoring of the dwellers of Madina, chapter on placing one's face against the grave of our Master the Prophet " and #9252 Book of Khilafa, "Chapter on the leadership of those unworthy of it"), and Ibn Hibban in Sahih. ]
It is important to note that Ibn Taymiyya and his student ad-Dhahabi have quoted this Hadith in their books which confirms that one can kiss the Grave and place one’s head on the Grave of Prophet Mohammad [sal Allahu alayhi wasallam] and Awliya Allah and request their mediation (Waseelah) after the death.