Vaishnava Samhita. Katha Sangraham. Vol III Book VI Chp 25 Shloka 2

प्रथमे हरिवंशस्तु राधादास्यपरायणः |
चकार शैशवे स्तोत्रं राधारससुधानिधिम्  ||

The First Chapter tells about Shri Harivamsha who considered service of Shri Krishna to be the only object of his life and completed a great work entitled "Radharasa Sudhanidhi" even in his young age.