The birth of Lord Narasimha is celebrated as Narasimha Jayanti. Lord Narasimha is the 4th avatar (incarnation) of Lord Vishnu. On the day of Narasimha Jayanti, Lord Vishnu came as Narasimha - half man and half animal- lion form to kill the demon king Hiranyakashipu.
Narasimha Jayanti is celebrated on the Vishaka Shukla Chaturdashi. (14th day of the waxing moon in the month of April- May) Devotees of Lord Narasimha observe fast on this day and visit temples of Lord Narasimha or Lord Vishnu. Devotees take only light food and break the fast on the next day, after performing the Visarjana puja (formal ending of a ritual). Devotees consider it auspicious if the festival comes on a Saturday with the combination of Swathi Nakshatra.
Narasimha is worshipped during the evening on the day of Vishaka Shukla Chaturdashi, as it is believed that Lord Narasimha appeared during evening to kill Hiranyakashipu. Jaggery and gram sprouts are offered as naivedhya to the Lord. Devotees also read the Narasimha avatar in the Bhagavada Purana.
Lord Vishnu incarnated as Narasimha, to protect Prahlada from his demonic father Hiranyakashipu. Hiranyakashipu wanted to become immortal. He undertook several rigorous penances at Mandarachala to please Lord Brahma. Appeased with Hiranyakashipu’s penance, Lord Brahma appeared before the king. The king asked Lord Brahma three boons to be granted; that he should not be killed by any human being or animal or demigod or by a living or non living being, he should not be killed either during day time or night, or inside or outside and should not be killed by any weapon. Lord Brahma granted all the three boons. With this the king became all powerful. He became a tyrant and started tormenting people. He conquered the entire universe and became invincible. He wanted his subjects to pray to him and not Lord Vishnu.
The gods wanted to put an end to his tyranny. Hiranyakashipu left behind his wife Gayathu, who was pregnant and went to Mandarachala to perform severe austerities. Taking advantage of Hiranyakashipu’s absence in the palace, the demigods, led by Lord Indra attacked the demons in the palace and arrested Gayathu. The demi gods wanted to kill the child as soon as it was born, but Narada Maharishi stopped Indra from killing the child and presaged that the child would become a great devotee of Lord Hari (Vishnu).
Narada Maharishi took Gayathu to his hermitage and imparted spiritual knowledge to her. The child in the womb attentively listened to the knowledge being imparted to its mother. When the child was born, he was named as Prahlada. He became a great devotee of Lord Vishnu. Hiranyakashipu appointed Chanda and Amarka, the two sons of Shukracharya for educating Prahlada. But Prahlada’s mind was always engrossed in the thought of Sri Hari and could not concentrate on what Chanda and Amarka were teaching. This enraged Hiranyakashipu and he decided to kill his son, Prahlada. The demons tried to kill Prahlada by throwing him under the feet of elephants, threw deadly weapons, threw him from the peak of a mountain, but nothing could kill him. Prahlada being an ardent devotee of Lord Vishnu was unscathed by the harsh treatment meted out to him. This only enraged Hiranyakashipu. Then he challenged Prahlada “where is your God”? to which Prahlada replied that He is everywhere. Then Hiranyakashipu, pointing to one of the pillars in the palace, asked his son, if God was in the pillar, to which his son answered “Yes He is”. Hiranyakashipu, at once struck the pillar forcefully and the pillar broke into pieces. Lord Sri Vishnu, appeared out of the pillar to corroborate the statement of His ardent devotee, Prahlada. Lord Hari (Vishnu), appeared as Narasimha from the pillar and killed the demon at twilight (neither day not night) by keeping the king on His lap( neither inside nor outside) with his nails. Thus Lord Vishnu did not violate any of the boons granted by Lord Brahma. Prahlada’s Smarana bhakti to Lord Vishnu is not only exemplary but also unparalleled.