Just like this question here, I would like to know whether any scripture portrays Lord Kartikeya (Murugan) to be the Supreme God.
Mahabharata: Vana Parva: Markandeya-Samasya Parva: Section CCXXX portrays Lord Kartikeya to be the Supreme God:
'Markandeya continued, "O valiant scion of Kuru's race, I shall now with due devotion pray to that unrivalled, mighty, six-faced, and valiant Guha who is worshipped by gods and Rishis, enumerating his other titles of distinction: do thou listen to them:
Thou art devoted to Brahma, begotten of Brahma, and versed in the mysteries of Brahma. Thou art called Brahmasaya, and thou art the foremost of those who are possessed of Brahma. Thou art fond of Brahma, thou art austere like the Brahmanas and art versed in the great mystery of Brahma and the leader of the Brahmanas. Thou art Swaha, thou art Swadha, and thou art the holiest of the holy, and art invoked in hymns and celebrated as the six-flamed fire.
Thou art the year, thou art the six seasons, thou art the months, the (lunar) half months, the (solar) declinations, and the cardinal points of space. Thou art lotus-eyed. Thou art possessed of a lily-like face. Thou hast a thousand faces and a thousand arms. Thou art the ruler of the universe, thou art the great Oblation, and thou art the animating spirit of all the gods and the Asuras. Thou art the great leader of armies. Thou art Prachanda (furious), thou art the Lord, and thou art the great master and the conqueror of thine enemies. Thou art, Sahasrabhu (multiform), Sahasratusti (a thousand times content), Sahasrabhuk (devourer of everything), and Sahasrapad (of a thousand legs), and thou art the earth itself.
Thou art possessed of infinite forms and thousand heads and great strength. According to thine own inclinations thou hast appeared as the son of Ganga, Swaha, Mahi, or Krittika. O six-faced god, thou dost play with the cock and assume different forms according to thy will. Thou art Daksha, Soma, the Maruta, Dharma, Vayu, the prince of mountains, and Indra, for all time.
Thou art mighty, the most eternal of all eternal things, and the lord of all lords. Thou art the progenitor of Truth, the destroyer of Diti's progeny (Asuras), and the great conqueror of the enemies of the celestials. Thou art the personation of virtue and being thyself vast and minute, thou art acquainted with the highest and lowest points of virtuous acts, and the mysteries of Brahma.
O foremost of all gods and high-souled lord of the Universe, this whole creation is over-spread with thy energy! I have thus prayed to thee according to the best of my power. I salute thee who art possessed of twelve eyes and many hands. Thy remaining attributes transcend my powers of comprehension!'