CC Madhya 15.166

kṛṣṇa sei satya kare, yei māge bhṛtya
bhṛtya-vāñchā-pūrti vinu nāhi anya kṛtya
Word for word: 
kṛṣṇa — Lord Kṛṣṇa; sei — that; satya kare — fulfills as true; yei — whatever; māge — wants; bhṛtya — servant; bhṛtya-vāñchā — the desire of His servant; pūrti — fulfilling; vinu — without; nāhi — there is not; anya — other; kṛtya — duty.
Translation: 
“Whatever a pure devotee wants from his master, Lord Kṛṣṇa doubtlessly grants because He has no duty other than to fulfill the desire of His devotee.