Alfred Lord Tennyson said "In the Spring a young man's fancy lightly turns to thoughts of love." Well, in the Summer a Brahmana's fancy lightly turns to thoughts of Avani Avittam! Avani Avittam, aka Upakarma, is a ritual performed on the Dakshinayana day in August where Brahmanas change their sacred thread. That's because traditionally you are supposed to begin Vedic study on the Dakshinayana day in August, and stop it on the Uttarayana day in January. And then you resume Vedic study in the next August. (Between January and August students would study subjects other than the Vedas.)
Proceeding at this pace, it would take 12 years to learn one Veda, and 48 years to learn all four. But in the Kali Yuga, students are not willing to wait so long to learn the Vedas, so violating scripture they learn the Vedas all year long. So the Avani Avittam ritual includes a Prayaschitta where you repent for not taking the mandatory break between January and August. Here'sthe procedure for it, from the Avani Avittam ritual I follow:
harirom tat। śrī govinda। govinda। govinda।
asya śrī bhagavata: mahāpuruṣasya śrīviṣṇorāgyayā pravartamānasya ādyabrahmaṇa:, dvitīya parārdhe, śrīśvetavarāha kalpe,vaivasvata manvantare, kali yuge, prathame pāde, jambūdvīpe, bhāratavarṣe, bharatakaṇḍe, śakābde, mero: dakṣiṇe pārśve, asmin vartamāne, vyāvahārike prabhavādi ṣaṣṭi saṃvatsarāṇāṃ madhye manmada nāmasaṃvatsare, dakṣiṇāyane, varṣa rutau, simha māse, śukla pakṣe, pourṇamāsyām śubhatithou, sthira vāsara, daniṣṭā nakṣatra yuktāyāṃ, śrī viṣṇu yoga, śrī viṣṇu karaṇa, śubha yoga, śubha karaṇa, evaṃguṇa viṣeṣaṇa viṣiṣṭāyām asyāṃ, pourṇamāsyām śubhatithou śrī bhagavadāgyayā bhagavat kainkarya rūpaṃ taiṣyām pourṇamāsyāṃ adhyāyotsarjana akaraṇa prāyaścittārthaṃ aṣṭottara sahasra/śata sankhyayā kāmokārṣīt manyurakārṣīt mahā mantra japaṃ kariṣye।
Then do japa (kāmokārṣit manyurakārśit) कामोकार्षीत् मन्युरकार्षीत् 1008 times or 108 times. After this do "mādhyāhnikam".
So as you can see, you are supposed to do Japam or repeated chanting of the mantra "kāmokārṣit manyurakārśit", which means "Desire did it, anger did it." The idea is that you are saying that desire and anger are what led you to commit the sin of not taking the mandatory break between January and August, and you are asking forgiveness for that sin.
Now the notion that desire and anger are the causes of sin is mentioned in chapter 2 of the Bhagavad Gita. But my question is, what scripture does the mantra "kāmokārṣit manyurakārśit" come from? It's referred to as a Mahamantra, so I assume it comes from some important scripture.