One verse

Srimad Bhagavatam 9.9.39

9.9.39

सा वै सप्त समा गर्भमबिभ्रन्न व्यजायत । जघ्नेऽश्मनोदरं तस्या: सोऽश्मकस्तेन कथ्यते ॥ ३९ ॥

sa vai sapta sama garbham abibhran na vyajayata jaghne ’smanodaram tasyah so ’smakas tena kathyate

sa
she, Queen Madayanti
vai
indeed
sapta
seven
samah
years
garbham
the child within the womb
abibhrat
continued to bear
na
not
vyajayata
gave delivery
jaghne
struck
asmana
by a stone
udaram
abdomen
tasyah
of her
sah
a son
asmakah
by the name Asmaka
tena
because of this
kathyate
was called.

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 ston).