When Chaitanya Mahaprabhu (b. 1486) wanted to be initiated into sannyas, the order of renunciates, he chose as his guru Keshava Bharati, who was a devotee of Lord Shiva. That was unusual because Chaitanya was a devotee of Lord Krishna.
In fact his followers accept Chaitanya as an incarnation of Krishna. We can find an explanation for his choice of sannyas guru in the pastimes of Krishna.
In a book by Jiva Goswami (b. 1513), Gopal-campu (Uttara-campu 8.10) we read:
“The young brothers Krishna and Balaram decided to go to a teacher and accept him as their guru. They said … ‘The best guru would be a person who is fixed in Brahman and worships Shiva … The great soul Sandipani of a dynasty from Kashi worships Shiva … he lives in Avanti, a place emanating happiness and near a Shiva temple. We should go there.'”
So Chaitanya was reprising his decision during his earlier Krishna pastimes to take initiation from a Shiva devotee. Moreover, we read in the book Gaura-ganoddesa-dipika by Kavi Karnapura (b. 1527) that Chaitanya’s sannyas guru Keshava Bharati was indeed a reincarnation of Krishna’s guru Sandipani Muni.
Ordinarily Krishna devotees and Shiva devotees go their separate ways. But Lord Krishna / Lord Chaitanya himself saw fit to bridge the gap. In doing so, he did not alter his personalist message to conform to the Shiva tradition’s impersonal one. Still, he honored the saint from a different teaching even to the extent of taking him as his initiating guru.
If all religious practitioners could adopt that ecumenical spirit, the world would be spared so much trouble.
