CC Madhya 10.145

sa śuśruvān mātari bhārgaveṇa
pitur niyogāt prahṛtaṁ dviṣad-vat
pratyagṛhīd agraja-śāsanaṁ tad
ājñā gurūṇāṁ hy avicāraṇīyā
Synonyms: 
saḥ — He (Lakṣmaṇa, the brother of Lord Rāmacandra); śuśruvān — hearing; mātari — unto the mother; bhārgaveṇa — by Paraśurāma; pituḥ — of the father; niyogāt — by the order; prahṛtam — killing; dviṣat-vat — like an enemy; pratyagṛhīt — accepted; agraja-śāsanam — the order of the elder brother; tat — that; ājñā — order; gurūṇām — of superior persons, such as the spiritual master or father; hi — because; avicāraṇīyā — to be obeyed without consideration.
Translation: 
“ ‘Being ordered by his father, Paraśurāma killed his mother, Reṇukā, just as if she were an enemy. When Lakṣmaṇa, the younger brother of Lord Rāmacandra, heard of this, He immediately engaged Himself in the service of His elder brother and accepted His orders. The order of the spiritual master must be obeyed without consideration.’
Purport: 

This is a quotation from the Raghu-vaṁśa (14.46). Lord Rāmacandra’s statement to Sītā given below is from the Rāmāyaṇa (Ayodhyā-kāṇḍa 22.9).