SB 10.66.30-31

dakṣiṇāgniṁ paricara
 brāhmaṇaiḥ samam ṛtvijam
 sa cāgniḥ pramathair vṛtaḥ
sādhayiṣyati saṅkalpam
 abrahmaṇye prayojitaḥ
ity ādiṣṭas tathā cakre
 kṛṣṇāyābhicaran vratī
dakṣiṇa-agnim — to the Dakṣiṇa fire; paricara — you should render service; brāhmaṇaiḥ — brāhmaṇas; samam — together with; ṛtvijam — the original priest; abhicāra-vidhānena — with the ritual known as abhicāra (meant for killing or otherwise harming an enemy); saḥ — that; ca — and; agniḥ — fire; pramathaiḥ — by the Pramathas (powerful mystics who are in Lord Śiva’s retinue and who assume many different forms); vṛtaḥ — surrounded; sādhayiṣyati — it will accomplish; saṅkalpam — your intention; abrahmaṇye — against one who is inimical to brāhmaṇas; prayojitaḥ — utilized; iti — so; ādiṣṭaḥ — instructed; tathā — in that way; cakre — he did; kṛṣṇāya — against Lord Kṛṣṇa; abhicaran — intending to do harm; vratī — observing the required vows.
Lord Śiva told him, “Accompanied by brāhmaṇas, serve the Dakṣiṇāgni fire — the original priest — following the injunctions of the abhicāra ritual. Then the Dakṣiṇāgni fire, together with many Pramathas, will fulfill your desire if you direct it against someone inimical to the brāhmaṇas.” So instructed, Sudakṣiṇa strictly observed the ritualistic vows and invoked the abhicāra against Lord Kṛṣṇa.

It is clearly stated here that the powerful Dakṣiṇāgni fire could be directed only against someone unfavorable to brahminical culture. Lord Kṛṣṇa, however, is most favorable to the brāhmaṇas and in fact maintains the brahminical culture. Lord Śiva thus knew that if Sudakṣiṇa attempted to direct the power of this ritual against Lord Kṛṣṇa, Sudakṣiṇa himself would perish.