In response to this request (Saubhari Rsi went to King Mandhata and begged for one of the King's daughters), the King said, "O brahmaṇa, any of my daughters may accept any husband according to her personal selection"
SB Canto 9
Saubhari Ṛṣi was engaged in austerity, deep in the water of the River Yamunā, when he saw a pair of fish engaged in sexual affairs. Thus he perceived the pleasure of sex life, and induced by this desire he went to King Māndhātā and begged for one of the King's daughters. In response to this request, the King said, "O brāhmaṇa, any of my daughters may accept any husband according to her personal selection."
This is the beginning of the story of Saubhari Ṛṣi. According to Viśvanātha Cakravartī Ṭhākura, Māndhātā was the king of Mathurā, and Saubhari Ṛṣi was engaged in austerity while submerged deep within the River Yamunā. When the ṛṣi felt sexual desire, he emerged from the water and went to King Māndhātā to ask that one of the King's daughters become his wife.