Mahabharata 9.2.4

वज्रसारमयं नूनं हृदयं सुदृढं ममयच्छ्रुत्वा निहतान्पुत्रान्दीर्यते न सहस्रधा

vajrasāramayaṃ nūnaṃ hṛdayaṃ sudṛḍhaṃ mamayacchrutvā nihatānputrāndīryate na sahasradhā

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