NOTE. Kaṇḍu Ṛṣi knew that killing a cow was adharma and yet he did it simply because his father ordered him to do so. Here is an instance of a powerful sage who is not affected by sinful reactions. The Āpastamba-dharma-sūtra (2.6.13.8) has this to say about such sages—teṣāṁ tejo-viśeṣeṇa pratyavāyo na vidyate: “Ancient sages incurred no sin [for transgressing dharma] on account of their extraordinary power.” So, by dint of his extraordinary powers, he didn’t lose his pious credits or purity of heart, etc.

As noted in Canto 1, Sagara Mahārāja had ordered his sons to get the Aśvamedha sacrificial horse. This was certainly a dhārmika order. But his sons were enthusiastic to do anything to fulfill this order; they went ahead and killed so many creatures—which was adhārmika—and so were punished by being burnt up by Lord Kapila’s glance. Yet, their ashes were washed by Gaṅgā and consequently they reached Svarga. So they didn’t lose anything in the long run by carrying out the dhārmika injunction of their father.

Regarding Paraśurāma killing his mother on the order of his father, it is clearly mentioned in Śrīmad-Bhāgavatam Canto 9 Chapter 16 that Paraśurāma did so because he understood that his father had the power to give his mother life and, in fact, Paraśurāma had Jamadagni give life back to Reṇukā. Again, nothing was lost in the long run by his obedience to his powerful father in an extra-ordinary circumstance.