Shiva Purana
ऋषय ऊचुः धौम्याग्रजेन शिशुना क्षीरार्थं हि तपः कृतम् ॥ तस्मात्क्षीरार्णवो दत्तस्तस्मै देवेन शूलिना ॥ १ ॥
The sages said:— It was for obtaining milk that penance was performed by the boy Upamanyu, the elder brother of Dhaumya. So an ocean of milk was granted to him by lord Śiva.
english translation
RSaya UcuH dhaumyAgrajena zizunA kSIrArthaM hi tapaH kRtam ॥ tasmAtkSIrArNavo dattastasmai devena zUlinA ॥ 1 ॥
hk transliteration by Sanscript