Many times people find it difficult to accept the fact that Krishna is the Original Supreme Personality of Godhead, and is the source of Vishnu and every demigod including Shiva and Brahma.
Keeping the sentimental debates aside, let us see a few of the many scriptural pieces of evidence that state Krishna is the Origin of Vishnu & all demigods.
KRISHNA: ORIGIN OF VISHNU
claims the Supreme Personality, Krishna, to be the origin of an auxiliary Personality of Godhead, Lord Vishnu.
From Him was born the Universal Form which sustained the mortal world. Making this Form as the substratum another celestial being was born, who is known as Vishnu. As soon as he was born, he multiplied himself into each of the universes. Later, he created this earth and then, the bodies of the living beings.
The Brahmas and other lords of the mundane worlds appear from the pores of the Maha-Vishnu and remain alive for the duration of His one exhalation. I adore the primeval Lord, Govinda, for Maha-Vishnu is a portion of His plenary portion of Him.
mentions the word of Shiva in which Shiva Himself reveals the original position of the Original Personality.
Lord Krishna who is eternally present in the Supreme Planet Goloka which is self-illuminating and benefactor of all devotional moods, is also residing in Vaikuntha (as Vaikuntha Narayana) and at Swetadwipa (as Kshirodakshayi Vishnu). Just as there is no difference between fire and its spark similarly there is no difference between Anshi (the origin of expansions, Lord Krishna) and Ansh (the expansion, Lord Vishnu).
describes Devaki’s prayer and confirms the related statement
My dear Krishna, I know that Maha-Vishnu, who is lying in the causal ocean of the cosmic manifestation, and who is the source of this whole creation, is simply an expansion of Your plenary portion. Creation, maintenance, and annihilation of this cosmic manifestation are being effected only by Your plenary portion. I am, therefore, taking shelter of You without any reservation.
mentions Narayana as Krishna's plenary portion
O Lord of lords, O Lord Krishna, You are the seer of all creation. You are indeed everyone’s dearest life. Are You not, therefore, my father, Narayana? The sacred name 'Narayana' refers to one whose abode is in the water born from Nara (that is Garbhodakashayi Vishnu). Indeed, that Narayana is also Your plenary portion. All Your plenary portions are transcendental. They are absolute and are not creations of Maya.
describes Krishna as Lord of all the three deities, Vishnu, Brahma and Shiva
O Lord Krishna, persons who are unaware of Your inconceivable energy cannot understand that You alone expand Yourself as the creator Brahma, maintainer Vishnu, and annihilator Shiva. Persons who are not in awareness of things as they contemplate that I, Brahma, am the creator, Vishnu is the maintainer, and Lord Shiva is the annihilator. Actually, You are alone everything: creator, maintainer and annihilator.
describes that Lord Krishna is the origin of the Purusha-Avatars, who are the creators of the material universes, is confirmed in the following prayer spoken by Bhishmadeva to Lord Krishna
Let me now invest my thinking, feeling and willing, which were so long engaged in different subjects and occupational duties, in the all-powerful Lord Shri Krishna. He is always self-satisfied, but sometimes, being the leader of the devotees, He enjoys transcendental pleasure by descending on the material world, although from Him only the material world is created.
confirms, where Narada Muni offers the following prayer
I offer my respectful obeisances to Lord Krishna, the all-knowing Original Personality of Godhead who, in order to liberate the conditioned souls, accepts the auspicious forms of His many incarnations.
also validates this in the following verse which was spoken by Nalakuvara and Manigriva to Lord Krishna
Appearing in bodies like those of an ordinary fish, tortoise and hog, You exhibit activities impossible for such creatures to perform: extraordinary, incomparable, transcendental activities of unlimited power and strength. These bodies of Yours, therefore, are not made of material elements but are incarnations of Your Supreme Personality.
mentions Krishna to be the origin of all Avataras in the following manner
The light of one candle being communicated to other candles, although it burns separately in them, is the same in its quality. I adore the primeval Lord Govinda who exhibits Himself equally in the same mobile manner in His various manifestations. We must understand that although all candles have the same potency, the original candle still retains its uniqueness. Krishna is like that original candle, the source of all incarnations.
confirms Krishna to be the origin of all Incarnations in the following verse spoken by Gargacharya to Nanda Maharaja
This son of yours, has many names and appears in different forms according to His transcendental qualities and activities. These are known to me, but people, in general, do not understand them.
mentions the following verse spoken by Brahma to Lord Krishna
O Original Personality of Godhead, O creator of the entire cosmic manifestation, although You never take birth, You nevertheless appear among the demigods, sages, human beings, animals, and aquatics, in order to crush the false pride of the demons, and bestow Your mercy to the saintly devotees.
repeats the similar facts in the following verse which was revealed by Lord Brahma
I worship Govinda, the primeval Lord, who manifested Himself personally as Krishna and the different avatars in the world in the forms of Rama, Nrisimha, Vamana, etc. as His subjective portions.
So in a short conclusion, we understand that Krishna is The Original God. Rest everything and everyone is emanating from Him.