Caitanya-caritāmṛta 5.124
eta mūrti-bheda kari’ kṛṣṇa-sevā kare kṛṣṇera śeṣatā pāñā ‘śeṣa’ nāma dhare
[eta moorti-bheda kari’ krishna-sevaa kare krishnera sheshataa paanaa ‘shesha’ naama dhare]
Blended reading (Sanskrit + English inline)
eta mūrti-bheda kari’ kṛṣṇa-sevā kare kṛṣṇera śeṣatā pāñā ‘śeṣa’ nāma dhare
He is thus called Lord Śeṣa, for He has attained the ultimate end of servitude to Kṛṣṇa. He takes many forms for the service of Kṛṣṇa, and thus He serves the Lord.
My note
Source: vedabase.io