Companions would kiss the grave of the Holy Prophet (Sallallahu alaihi wa sallam)
There is a Hadith in Musnad Imam Ahmed, Mustadrak ‘Alas Sahihain, Majma Uz Zawaaid, Subul Ul Huda War Rashad, etc.
Translation of Hadith: It is narrated on the authority of Hadhrat Dawood Bin Saleh (May Allah be well pleased with them), he said that once Marwan saw that a person had kept his face on the blessed grave of the Holy Prophet (Sallallahu alaihi wa sallam). Marwan asked: What are you doing? When he went forward, he saw that that person was Hadhrat Abu Ayyub Ansari (May Allah be well pleased with him). He said: Yes! I have come to pay my respects to the Holy Prophet (Sallallahu alaihi wa sallam), I have not come to any piece of stone. I have heard the Holy Prophet (Sallallahu alaihi wa sallam) saying: You don’t cry over the Deen when a person fit for it rules over it, however, you may cry over Deen when somebody not fit for it rules over it.
This Hadith is mentioned in the following books:
Musnad Imam Ahmed, Hadith No. 24302,
Mustadrak ‘Alas Sahihain, Hadith No. 8717,
Majma Uz Zawaaid, Hadith No. 5845,
Subul Ul Huda War Rashad, Vol. 12, Pg. No. 398)