Shiva Purana
सनकः सनातनश्चैव प्रभुर्यश्च सनन्दनः ॥ विभुः सनत्कुमारश्च निर्मलो निरहंकृतिः ॥२२॥
They are Sanaka, Sanātana, Sanandana and Sanatkumāra freed from sin and egotism.
english translation
sanakaH sanAtanazcaiva prabhuryazca sanandanaH ॥ vibhuH sanatkumArazca nirmalo nirahaMkRtiH ॥22॥
hk transliteration by Sanscript