It is usually believed that tapping temples on forehead five times with closed fists, accompanied with the recitation of the "Suklambaradharam..." sloka is a shortcut method of worshiping Lord Mahaganapaty.
Since Mahaganapaty is to be worshiped first, many rituals, including Sandhyavandanam, employ this shortcut.
Quoting from this page:
- Vighnesvara Dhyanam Meditation on Lord Vighnesvara
While reciting the following mantra, gently tap the two sides of the forehead with the fists five times with the thought that thereby the nectar (amruta) in the head flows down through all the nerves and invigorates them.
Shuklambaradharam Vishnum Sasivarnam Chaturbhujam, Prasannavadanam dhyayeh, Sarva-vighnopasantaye
It is believed that the Soma ,as a result of the tapping, flows down from the Sahasrara chakra to bath Ganapaty who is seated below in the Muladhara Chakra.
Here is a video demonstrating the the process (move to 2.37 mins).
Question-Which scriptures mention about this process?
Note-I am only asking about the process here & not about the sloka "Suklaambaradharam..."