Thawban was one of the freed slave of Holy Prophet of Islam (pbuh). He was always with the Prophet (pbuh) at home or in journey. After the passing away of the Prophet (pbuh) he stayed for some years in Syria and later for some time in Egypt. He was present at the time of the victory on Egypt. Thawbaan died at the age of 51.
It is found in rewayaat that he adored the Holy Prophet (pbuh) so much that for a single moment he could not bear his absence. One day Holy Prophet (pbuh) saw him in a very sad mood. He appeared to be weak. Prophet (pbuh) asked him, "O' Thawbaan! What has happened to you? Thawbaan replied:"O Messenger of Allah! I am not ill nor have any pain, but, I am worried about your proximity which I will be missing in the Paradise. As you will be in a higher station and I in a lower position. I will not be be able to see you over there."
At the same moment an Aayat was revealed. " And whoso obeys Allah and the Messenger (Muhammad ), then they will be in the company of those on whom Allah has bestowed His Grace, of the Prophets, the Siddiqin, the martyrs, and the righteous. And how excellent these companions are! " (surah Nisa, aayat 69)
(Biharul Anwaar vol.2 pg. 68)