Bhakti-rasāmṛta-sindhu .2.93
Blended reading (Sanskrit + English inline)
Now, the total regulative principles come to an aggregate of sixty-four items. As we have mentioned, the first are the primary ten regulative principles. Then come the secondary ten regulative principles, and added to these are forty-four other activities. So all together there are sixty-four items for discharging the regulative practice of devotional service. Out of these sixty-four items, five items—namely worshiping the Deity, hearing Śrīmad-Bhāgavatam, associating among the devotees, saṅkīrtana, and living in Mathurā—are very important. The sixty-four items of devotional service should include all of our activities of body, mind and speech. As stated in the beginning, the regulative principle of devotional service enjoins that all of our senses must be employed in the service of the Lord. Exactly how they can be thus employed is described in the above sixty-four items. Now, Śrīla Rūpa Gosvāmī will give evidence from different scriptures supporting the authenticity of many of these points.
These are the sixty-four types of worship involving the body, senses and internal organ. Some items such as surrendering to the feet of guru should be considered as single items with no divisions. Others such as deity worship and kīrtana have many internal divisions. [Note: As explained later there are guṇa-kīrtana, līlā-kīrtana as well as nāma-kīrtana. Like musical works, these are often divided up into parts.] Those are considered as one aṅga from considering the whole. Though one can find many aṅgas within deity worship or other items, they can also be considered as a whole unit and regarded as one item. Thus there is no contradiction to counting sixty-four items only.
My note
Source: vedabase.io