Lord Nityananda considered that since Lord Chaitanya was the Supreme Personality of Godhead, He broke the Lord Chaitanya’s sannayasa danda in three parts. Lord Nityananda then threw the three parts of danda in the Ganges.
Reference:- https://kids.iskcondesiretree.com/eBooks/Chaitanya_Charitamrita/Chaitanya_Charitamrita.pdf