As per this wikipedia article Brahma Rakshasha are Sprit with quality of brahmin as well as Rakshasha. Can someone please tell what is
Brahma Rakshasa is found at least in the following sources:
Padma Purana, chapter 5.7, where Ravana is said to be of a Brahma-Rakshasa class:
[...] O great king, you yourself are that great god Viṣṇu, who destroys the misery of gods, and who has taken up a (human) form. O highly intelligent one, this Bharata, Lakṣmaṇa and Śatrughna are (born) from your portion. So also is Rāvaṇa who troubles the gods created. Due to the continuity of former enmity he kidnapped Sītā, O king. You killed that demon born in the stock of a brāhmaṇa demon.
Source (English, Sanskrit)
In Padma Purana chapter 5.115, the Brahma-Rakshasas are described as knowers the Vedas but ignorant of the Pruanas:
Those preceptors who are regarded as knowers of the hymns and Vedas, are not capable of giving all knowledge. Therefore, they are not teachers. O Rāma, generally goblins who are the ghosts of brāhmaṇas know the Vedic hymns, and not ones who know the Purāṇas. All who are averse to Purāṇas do not see (i.e. know) everything. Therefore, one who knows Purāṇas is a master who destroys sins.
Source (English, Sanskrit)
However, the last reference should be understood in the context of a ghost. The following sub-story illustrates in the chapter 5.116:
Once when Rāma was playing, a stormy wind knocked him down, and he fell down crying. In the meanwhile the ghost of a brāhmaṇa seized Rāma and he fainted. Then the boy, his companion, crying hither and thither, informed the king of Rāma in that condition. Then the king took Rāma and spoke to Vasiṣṭha. He asked him: “What is this (that has happened) to Rāma?” Then Vasiṣṭha took sacred ash, consecrated it, and got rid of that ghost of the brāhmaṇa. He asked him: “Who are you?” and he said: “I am a brāhmaṇa, proud of (my knowledge of) the Vedas. Having frequently snatched away the wealth of others, I became a Brahma-ghost. Think of my acquittance.”
Source
Another chapter, 6.182 narrates how a couple turned into Brahma Rakshasas:
8-17. There was a brāhmaṇa, Kuśīvala by name, who knew the essential nature of the Vedas and Vedāṅgas, who was proficient in all holy texts, and whose conduct was good. His wife, named Kumati, was of a wicked mind. He along with his wife, was very greedy and accepted great gifts like a buffalo, a Kālapuruṣa(?), horses etc., day after day; (but) he did not give (even) a chowrie to brāhmaṇas. As time passed, the two evil spirits, of the form of brāhmaṇa-ghosts, with their bodies oppressed by hunger and thirst, roamed over this earth. They then rested after having come to the root of the palm tree.
Source
According to the Shiva Purana, chapter 2.2.26, one becomes a Brahamana-Rakshasa “due to their acceptance of monetary gifts from undeserving persons”
33-36. You are engaged in discussing Vedas but you will be ignorant of Vedic principles. May these brahmins prattle that there is nothing else. May these brahmins indulging in lust, heavenly pleasures, anger, covetousness and pride be shameless beggars. These brahmins will be officiating in the sacrifices of Śūdras, following the Vedic path. They will be perpetually poor and eager to receive monetary gifts. Due to their acceptance of monetary gifts from undeserving persons they will fall into hell. O Dakṣa, some of them will become brahminical Rākṣasas.
Source (English, Sanskrit)
For further study see the following pages:
https://www.wisdomlib.org/definition/brahmarakshasa
The Katha-Sarit-Sagara also includes some chapters involving Brahma-Rakshasas:
Chapter 6.6-7
Chapter 12.9
Chapter 12.27
The last chapter describes the physical apperance of a Brahma-Rakshasa:
At that moment there suddenly came there a Brāhman demon, black as soot, with hair yellow as the lightning, looking like a thunder-cloud. He had made himself a wreath of entrails; he wore a sacrificial cord of hair; he was gnawing the flesh of a man’s head, and drinking blood out of a skull. The monster, terrible with projecting tusks, uttered a horrible loud laugh, and vomiting fire with rage, menaced the king in the following words: [...]
There is a South-Indian folk-tale which involves summoning a Brahma-Rakshasa:
a landowner who learnt an incantation by means of which he summoned a Brahma-Rakshasa, who became his servant, at the same time informing him that if he failed to provide work the Rakshasa would kill him. Everything he could think of was done in an incredibly short time—tank repaired and deepened, lands all cultivated—and there being nothing more to be done the wife gave the demon a hair of her head to straighten. He failed to do it, but remembering that goldsmiths heated wires when about to straighten them, he placed the hair on a fire, which burnt it up. He was afraid to face his mistress after it, so he ran away.
Source
In a different (less spiritual) cultural context, a “Brahma-Rakshasa” refers to a “Brahmana defeated in disputations”. (see: Indian Epigraphical Glossary).
