SB 1.7.38

pratiśrutaṁ ca bhavatā
 pāñcālyai śṛṇvato mama
āhariṣye śiras tasya
 yas te mānini putra-hā
Synonyms: 
pratiśrutam — it is promised; ca — and; bhavatā — by you; pāñcālyai — unto the daughter of the King of Pāñcāla (Draupadī); śṛṇvataḥ — which was heard; mama — by Me personally; āhariṣye — must I bring; śiraḥ — the head; tasya — of him; yaḥ — whom; te — your; mānini — consider; putra- — the killer of your sons.
Translation: 
Furthermore, I have personally heard you promise Draupadī that you would bring forth the head of the killer of her sons.