CC Ādi 6.29

bhakti-upadeśa vinu tāṅra nāhi kārya
ataeva nāma haila ‘advaita ācārya’
Word for word: 
bhakti-upadeśa — instruction of devotional service; vinu — without; tāṅra — His; nāhi — there is not; kārya — occupation; ataeva — therefore; nāma — the name; haila — became; advaita ācārya — the supreme teacher (ācārya) Advaita Prabhu.
Translation: 
Since He has no other occupation than to teach devotional service, His name is Advaita Ācārya.