He [Aśvatthāmā] had already lost his bodily luster due to infanticide, and now, moreover, having lost the jewel from his head, he lost even more strength. Thus he was unbound and driven out of the camp.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
विमुच्य रशनाबद्धं बालहत्याहतप्रभम् । तेजसा मणिना हीनं शिबिरान्निरयापयत्
vimucya raśanābaddhaṃ bālahatyāhataprabham | tejasā maṇinā hīnaṃ śibirānnirayāpayat
SB 1.7.56