Mahabharata 1.172.4

न हि तं वारयामास वसिष्ठो रक्षसां वधात्द्वितीयामस्य मा भाङ्क्षं प्रतिज्ञामिति निश्चयात्

na hi taṃ vārayāmāsa vasiṣṭho rakṣasāṃ vadhātdvitīyāmasya mā bhāṅkṣaṃ pratijñāmiti niścayāt

Our plain-language meaning of this verse is waiting for scholar review.