The prophetic Sunnah contains established, authentic practices.
Placing one's hand on the area of pain while supplicating is one of them.
It is narrated on the authority of 'Uthman Ibn Abi al-'As (may Allah be pleased with him)
that he complained to the Messenger of Allah (peace and blessings of Allah be upon him) about a pain he had felt in his body ever since he embraced Islam.
The Messenger of Allah (peace and blessings of Allah be upon him) said to him:
"Place your hand on the part of your body that hurts and say, 'In the name of Allah' three times,
and say seven times, 'I seek refuge in Allah and His power from the evil of what I feel and fear.'"
Narrated by Muslim.