King Gadhi’s wife gave birth to Kaushika, who became sage Vishvamitra. Gadhi was not the biological father.
Gadhi’s daughter Satyavati was married with sage Richika. She asked for a mixture for herself und her mother to have children.
Richika mixed a drink for the queen to give birth to a ruler (Kshatriya) and one for Satyavati, to give birth to a sage (Brahmana). The mother exchanged the fessels with the mixture. The queen gave birth to a sage, Kaushika, and Satyavati to a ruler, Jamadagni.