tabe nityananda-gosanira vyasa-pujana
nityanandavese kaila musala dharana

Translation
Nityananda Prabhu then arranged to offer Vyasa-puja, or worship of the spiritual master, to Lord Sri Gaurasundara. But Lord Caitanya carried the plowlike weapon called musala in the ecstasy of being Nityananda Prabhu.

Purport
By the order of Sri Caitanya Mahaprabhu, Nityananda Prabhu arranged for the Vyasa-puja of the Lord on the night of the full moon. He arranged for the Vyasa-puja, or guru-puja, through the agency of Vyasadeva. Since Vyasadeva is the original guru (spiritual master) of all who follow the Vedic principles, worship of the spiritual master is called Vyasa-puja. Nityananda Prabhu arranged for the Vyasa-puja, and sankirtana was going on, but when He tried to put a garland on the shoulder of Sri Caitanya Mahaprabhu, He saw Himself in Lord Caitanya. There is no difference between the spiritual positions of Lord Caitanya Mahaprabhu and Nityananda Prabhu, or Krsna and Balarama. All of Them are but different manifestations of the Supreme Personality of Godhead. During this special ceremony, all the devotees of Lord Caitanya Mahaprabhu could understand that there is no difference between Lord Caitanya and Nityananda Prabhu.

Srila A.C. Bhaktivedanta Swami Prabhupada
Caitanya-Caritamrta Adi 17.16