Srimad Bhagavatam Canto 05, Chapter 20, Text 44

SB 5.20.44

mrte ’nda esa etasmin yad abhut tato martanda iti vyapadesah; hiranyagarbha iti yad dhiranyanda-samudbhavah.
 
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
The sun-god is also known as Vairaja, the total material body for all living entities. Because he entered this dull egg of the universe at the time of creation, he is also called Martanda. He is also known as Hiranyagarbha because he received his material body from Hiranyagarbha [Lord Brahma].
 
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
The post of Lord Brahma is meant for very highly elevated, spiritually advanced living beings. When such living beings are unavailable, Lord Visnu, the Supreme Personality of Godhead, expands Himself as Lord Brahma. This takes place very rarely. Consequently there are two kinds of Brahmas. Sometimes Brahma is an ordinary living entity, and at other times Brahma is the Supreme Personality of Godhead. The Brahma spoken of here is an ordinary living being. Whether Brahma is the Supreme Personality of Godhead or an ordinary living being, he is known as Vairaja Brahma and Hiranyagarbha Brahma. Therefore the sun-god is also accepted as Vairaja Brahma.
Srimad Bhagavatam Canto 05, Chapter 20, Text 43
Srimad Bhagavatam Canto 05, Chapter 20, Text 45