CC Ādi 13.70

kṛṣṇa avatārite ācārya pratijñā kariyā
kṛṣṇa-pūjā kare tulasī-gaṅgājala diyā
Synonyms: 
kṛṣṇa — Lord Kṛṣṇa; avatārite — to cause His advent; ācārya — Advaita Ācārya; pratijñā — promise; kariyā — making; kṛṣṇa-pūjā — worship of Lord Kṛṣṇa; kare — does; tulasī — tulasī leaves; gaṅgā-jala diyā — with the water of the Ganges.
Translation: 
With this consideration, Advaita Ācārya Prabhu, promising to cause Lord Kṛṣṇa to descend, began to worship the Supreme Personality of Godhead, Kṛṣṇa, with tulasī leaves and water of the Ganges.
Purport: 

Tulasī leaves and Ganges water, with, if possible, a little pulp of sandalwood, is sufficient paraphernalia to worship the Supreme Personality of Godhead. The Lord says in the Bhagavad-gītā (9.26):

patraṁ puṣpaṁ phalaṁ toyaṁyo me bhaktyā prayacchati
tad ahaṁ bhakty-upahṛtam
aśnāmi prayatātmanaḥ

“If one offers Me with love and devotion a leaf, a flower, a fruit or water, I will accept it.” Following this principle, Advaita Prabhu pleased the Supreme Personality of Godhead with tulasī leaves and water of the Ganges.