SB 9.2.1

śrī-śuka uvāca
evaṁ gate ’tha sudyumne
 manur vaivasvataḥ sute
putra-kāmas tapas tepe
 yamunāyāṁ śataṁ samāḥ
Word for word: 
śrī-śukaḥ uvāca — Śrī Śukadeva Gosvāmī said; evam — thus; gate — had accepted the order of vānaprastha; atha — thereafter; sudyumne — when Sudyumna; manuḥ vaivasvataḥ — Vaivasvata Manu, known as Śrāddhadeva; sute — his son; putra-kāmaḥ — desiring to get sons; tapaḥ tepe — executed severe austerities; yamunāyām — on the bank of the Yamunā; śatam samāḥ — for one hundred years.
Translation: 
Śukadeva Gosvāmī said: Thereafter, when his son Sudyumna had thus gone to the forest to accept the order of vānaprastha, Vaivasvata Manu [Śrāddhadeva], being desirous of getting more sons, performed severe austerities on the bank of the Yamunā for one hundred years.