Srimad Bhagavatam Canto 05, Chapter 18, Text 21

SB 5.18.21

ya tasya te pada-saroruharhanam
 nikamayet sakhila-kama-lampata
tad eva rasipsitam ipsito ’rcito
 yad-bhagna-yacña bhagavan pratapyate
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
My dear Lord, You automatically fulfill all the desires of a woman who worships Your lotus feet in pure love. However, if a woman worships Your lotus feet for a particular purpose, You also quickly fulfill her desires, but in the end she becomes broken-hearted and laments. Therefore one need not worship Your lotus feet for some material benefit.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
Srila Rupa Gosvami describes pure devotional service as anyabhilasita-sunyam jñana-karmady-anavrtam. One should not worship the Supreme Personality of Godhead to fulfill some material desire for success in fruitive activities or mental speculation. To serve the lotus feet of the Lord means to serve Him exactly as He desires. The neophyte devotee is therefore ordered to worship the Lord strictly according to the regulative principles given by the spiritual master and the sastras. By executing devotional service in that way, he gradually becomes attached to Krsna, and when his original dormant love for the Lord becomes manifest, he spontaneously serves the Lord without any motive. This condition is the perfect stage of one’s relationship with the Lord. The Lord then looks after the comfort and security of His devotee without being asked. Krsna promises in Bhagavad-gita (9.22):
ananyas cintayanto mam
 ye janah paryupasate
tesam nityabhiyuktanam
 yoga-ksemam vahamy aham
The Supreme Lord personally takes care of anyone who is completely engaged in His devotional service. Whatever he has, the Lord protects, and whatever he needs, the Lord supplies. Therefore why should one bother the Lord for something material? Such prayers are unnecessary.
Srila Visvanatha Cakravarti Thakura explains that even if a devotee wishes the Lord to fulfill a particular desire, the devotee should not be considered a sakama-bhakta (a devotee with some motive). In the Bhagavad-gita (7.16) Krsna says:
catur-vidha bhajante mam
 janah sukrtino ’rjuna
arto jijñasur artharthi
 jñani ca bharatarsabha
“O best among the Bharatas [Arjuna], four kinds of pious men render devotional service unto Me — the distressed, the desirer of wealth, the inquisitive and he who is searching for knowledge of the Absolute.” The arta and the artharthi, who approach the Supreme Personality of Godhead for relief from misery or for some money, are not sakama-bhaktas, although they appear to be. Being neophyte devotees, they are simply ignorant. Later in Bhagavad-gita the Lord says, udarah sarva evaite: they are all magnanimous (udarah). Although in the beginning a devotee may harbor some desire, in due course of time it will vanish. Therefore the Srimad-Bhagavatam enjoins:
akamah sarva-kamo va
 moksa-kama udara-dhih
tivrena bhakti-yogena
 yajeta purusam param
“A person who has broader intelligence, whether he is full of all material desire, is free from material desire, or has a desire for liberation, must by all means worship the supreme whole, the Personality of Godhead.” (Bhag. 2.3.10)
Even if one wants something material, he should pray to no one but the Lord to fulfill his desire. If one approaches a demigod for the fulfillment of his desires, he is to be considered nasta-buddhi, bereft of all good sense. Krsna says in Bhagavad-gita (7.20):
kamais tais tair hrta-jñanah
 prapadyante ’nya-devatah
tam tam niyamam asthaya
 prakrtya niyatah svaya
“Those whose minds are distorted by material desires surrender unto demigods and follow the particular rules and regulations of worship according to their own natures.”
Laksmidevi advises all devotees who approach the Lord with material desires that according to her practical experience, the Lord is Kamadeva, and thus there is no need to ask Him for anything material. She says that everyone should simply serve the Lord without any motive. Since the Supreme Personality of Godhead is sitting in everyone’s heart, He knows everyone’s thoughts, and in due course of time He will fulfill all desires. Therefore let us completely depend on the service of the Lord without bothering Him with our material requests.
Srimad Bhagavatam Canto 05, Chapter 18, Text 20
Srimad Bhagavatam Canto 05, Chapter 18, Text 22