Srimad Bhagavatam Canto 09, Chapter 09, Text 39

SB 9.9.39

sa vai sapta sama garbham
 abibhran na vyajayata
jaghne ’smanodaram tasyah
 so ’smakas tena kathyate
 
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada: 
 
Madayanti bore the child within the womb for seven years and did not give birth. Therefore Vasistha struck her abdomen with a stone, and then the child was born. Consequently, the child was known as Asmaka [“the child born of a stone”].
Srimad Bhagavatam Canto 09, Chapter 09, Text 38
Srimad Bhagavatam Canto 09, Chapter 09, Text 40