Srimad Bhagavatam Canto 04, Chapter 22, Text 06

SB 4.22.6

hatakasana asinan
sva-dhisnyesv iva pavakan
sraddha-samyama-samyuktah
pritah praha bhavagrajan
 
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
 
The four great sages were elder to Lord Siva, and when they were seated on the golden throne, they appeared just like fire blazing on an altar. Maharaja Prthu, out of his great gentleness and respect for them, began to speak with great restraint as follows.
 
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
 
The Kumaras are described herein as the elder brothers of Lord Siva. When the Kumaras were born out of the body of Lord Brahma, they were requested to get married and increase the population. In the beginning of the creation there was a great need of population; therefore Lord Brahma was creating one son after another and ordering them to increase. However, when the Kumaras were requested to do so, they declined. They wanted to remain brahmacari throughout life and be engaged fully in the devotional service of the Lord. The Kumaras are called naisthika-brahmacari, meaning they are never to marry. Because of their refusal to marry, Lord Brahma became so angry that his eyes became reddish. From between his eyes, Lord Siva, or Rudra, appeared. The mode of anger is consequently known as rudra. Lord Siva also has a sampradaya party, known as the Rudra sampradaya, and they are also known as Vaisnavas.
 
Srimad Bhagavatam Canto 04, Chapter 22, Text 05
Srimad Bhagavatam Canto 04, Chapter 22, Text 07