Srimad Bhagavatam Canto 06, Chapter 09, Text 40

SB 6.9.40

tri-bhuvanatma-bhavana trivikrama tri-nayana tri-loka-manoharanubhava tavaiva vibhutayo ditija-danujadayas capi tesam upakrama-samayo ’yam iti svatma-mayaya sura-nara-mrga-misrita-jalacarakrtibhir yathaparadham dandam danda-dhara dadhartha evam enam api bhagavañ jahi tvastram uta yadi manyase.
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
O Lord, O personified three worlds, father of the three worlds! O strength of the three worlds, in the form of the Vamana incarnation! O three-eyed form of Nrsimhadeva! O most beautiful person within the three worlds! Everything and everyone, including human beings and even the Daitya demons and the Danavas, is but an expansion of Your energy. O supremely powerful one, You have always appeared in Your forms as the various incarnations to punish the demons as soon as they become very powerful. You appear as Lord Vamanadeva, Lord Rama and Lord Krsna. You appear sometimes as an animal like Lord Boar, sometimes a mixed incarnation like Lord Nrsimhadeva and Lord Hayagriva, and sometimes an aquatic like Lord Fish and Lord Tortoise. Assuming such various forms, You have always punished the demons and Danavas. We therefore pray that Your Lordship appear today as another incarnation, if You so desire, to kill the great demon Vrtrasura.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
There are two kinds of devotees, known as sakama and akama. Pure devotees are akama, whereas devotees in the upper planetary systems, such as the demigods, are called sakama because they still want to enjoy material opulence. Because of their pious activities, the sakama devotees are promoted to the higher planetary systems, but at heart they still desire to lord it over the material resources. The sakama devotees are sometimes disturbed by the demons and Raksasas, but the Lord is so kind that He always saves them by appearing as an incarnation. The Lord’s incarnations are so powerful that Lord Vamanadeva covered the entire universe with two steps and therefore had no place for His third step. The Lord is called Trivikrama because He showed His strength by delivering the entire universe with merely three steps.
The difference between sakama and akama devotees is that when sakama devotees, like the demigods, fall into difficulty, they approach the Supreme Personality of Godhead for relief, whereas akama devotees, even in the greatest danger, never disturb the Lord for material benefits. Even if an akama devotee is suffering, he thinks this is due to his past impious activities and agrees to suffer the consequences. He never disturbs the Lord. Sakama devotees immediately pray to the Lord as soon as they are in difficulty, but they are regarded as pious because they consider themselves fully dependent on the mercy of the Lord. As stated in Srimad-Bhagavatam (10.14.8):
tat te ’nukampam susamiksamano
 bhuñjana evatma-krtam vipakam
hrd-vag-vapurbhir vidadhan namas te
 jiveta yo mukti-pade sa daya-bhak
Even while suffering in the midst of difficulties, devotees simply offer their prayers and service more enthusiastically. In this way they become firmly fixed in devotional service and eligible to return home, back to Godhead, without a doubt. Sakama devotees, of course, achieve from the Lord the results they desire from their prayers, but they do not immediately become fit to return to Godhead. It is to be noted herein that Lord Visnu, in His various incarnations, is always the protector of His devotees. Srila Madhvacarya says: vividham bhava-patratvat sarve visnor vibhutayah. Krsna is the original Personality of Godhead (krsnas tu bhagavan svayam). All the other incarnations proceed from Lord Visnu.
Srimad Bhagavatam Canto 06, Chapter 09, Text 39
Srimad Bhagavatam Canto 06, Chapter 09, Text 41