Rig Veda 1.84.13

Sanskrit text [Accents, Plain, Transliterated]:

इन्द्रो॑ दधी॒चो अ॒स्थभि॑र्वृ॒त्राण्यप्र॑तिष्कुतः । ज॒घान॑ नव॒तीर्नव॑ ॥
इन्द्रो दधीचो अस्थभिर्वृत्राण्यप्रतिष्कुतः । जघान नवतीर्नव ॥
indro dadhīco asthabhir vṛtrāṇy apratiṣkutaḥ | jaghāna navatīr nava ||

English translation:

“Indra, with the bones of Dadhīci, slew ninety times nine Vṛtras.”

Commentary by Sāyaṇa: Ṛgveda-bhāṣya

Dadhyañc = Dadhīca and Dadhīci, a sage. His bones formed the thunderbolt of Indra. dadhyañc, son of Atharvan, like the asuras, was intimidated and tranquilized by his appearance; but, when he went to svarga, the asuras overspread the whole earth. Indra, inquiring what had become of him and if something of him was left  behind, was told that the horse's head with which he had at one time taught the madhuvidyā to the aśvins, was somewhere in existence, but no one knew where. After a searth, it was found in the lake Śaryaṇāvat, near Kurukṣetra. With the bones of the skull, Indra slew the asuras (i.e. foiled the nine times ninety or eight hundred and ten, strategems or devices of the asuras or Vṛtras]. The number is accounted for by the legend that in the beginning, the āsurī māyā (demoniac illusion) was practised in the three worlds, for three periods (past, present, and future), thus becoming nine-fold; each was exerted with three śaktis or energies, thus becoming twenty seven; each was again modified by the three guṇas, thus becoming eighty-one; the scene of their display extended to each of the ten regions of space, thus becoming the nine times ninety of the text, or 810

Details:

Ṛṣi (sage/seer): gotamo rāhūgaṇaḥ [gotama rāhūgaṇa];
Devatā (deity/subject-matter): indra:;
Chandas (meter): nicṛdgāyatrī ;
Svara (tone/note): Swar;

Padapatha [Accents, Plain, Transliterated]:

इन्द्रः॑ । द॒धी॒चः । अ॒स्थऽभिः॑ । वृ॒त्राणि॑ । अप्र॑तिऽस्कुतः । ज॒घान॑ । न॒व॒तीः । नव॑ ॥
इन्द्रः । दधीचः । अस्थभिः । वृत्राणि । अप्रतिस्कुतः । जघान । नवतीः । नव ॥
indraḥ | dadhīcaḥ | astha-bhiḥ | vṛtrāṇi | aprati-skutaḥ | jaghāna | navatīḥ | nava

Multi-layer Annotation of the Ṛgveda

[Rigveda 1.84.13 English analysis of grammar]