Gayatri Japam
Source - https://hindupad.com/gayatri-japa-day-rig-upakarma/
Gayatri Japa Day (Gayatri Japam Sankalpam) is observed on the next day of Purnima, Full Moon day in Shravana month
It is the most auspicious day to chant the Supreme of all the mantras, the sacred Gayatri Mantra. Gayathri is the Supreme Goddess and considered as the Mother Goddess. Gayatri Mantra is the foundation and the theme for every mantra in Hinduism. Gayatri Japam day is also popular as Gayatri Pratipada or Gayatri Padyami
Gayatri Japam is recited on this day by all Brahmins in South India (Yajurveda, Rig Veda, and Sama Veda Brahmins)
On Gayatri Japa Day, all the Hindus mainly Brahmins recite Gayathri Mantra. Any Hindu, celibate (Brahmachari), the Grihastha (householder) or the Vanaprastha (old people) have to chant Gayatri Mantra on Gayatri Japa Day. But nowadays only Brahmins are observing the Gayatri Japam. During Avani Avittam or Raksha Bandhan, Gayatri Japam is recited. Brahmins who wear the sacred thread, Jandhyam or Janeyu or Yagnopaveeta or Janivar, recite the Gayathri Mantra for 108 times
On this day, it is advised to recite this mantra 1008 times
Gayatri Mantram:
Om bhur bhuvah svah
Tat savitur varenyam
Bhargo devasya dheemahi
Dhiyo yo nah prachodayaat