Śrīmad-Bhāgavatam · Text 1.7.18
Who is speaking and story frame
तमापतन्तं स विलक्ष्य दूरात्
कुमारहोद्विग्नमना रथेन ।
पराद्रवत्प्राणपरीप्सुरुर्व्यां
यावद्गमं रुद्रभयाद्यथा क: ॥ १८ ॥
tam āpatantaṁ sa vilakṣya dūrāt
kumāra-hodvigna-manā rathena
parādravat prāṇa-parīpsur urvyāṁ
yāvad-gamaṁ rudra-bhayād yathā kaḥ
Aśvatthāmā, the murderer of the princes, seeing from a great distance Arjuna coming at him with great speed, fled in his chariot, panic stricken, just to save his life, as Brahmā fled in fear from Śiva.
Read Śrīla Prabhupāda's purport on Vedabase.io