It is neither.
The origin of folding the hands at prayer is virtually unknown and a version of folded hands can be found in use by followers of many world religions.
For instance, in the Buddhist tradition, “…The posture for prayer (kneeling and hands neatly placed palm-to-palm below the chin) has a long history, and is also used in worship…”
In Hinduism, mudras (special hand gestures) are used to receive and gather an alleged energy that is said to inhabit the universe. While there are many different kinds of mudras, one of these – the anjali mudra – is bringing the palms of the hands together over the heart.
“The prayerful hand position is a mudra called anjali, from the root anj, ‘to adorn,’ ‘honor,’ ‘celebrate.’ The hands held in union signify the oneness of an apparently dual cosmos, the bringing together of spirit and matter, or the self meeting the Self.”
The Japanese native religion known as Shinto also uses folded hands in prayer. “…[T]he gesture known as ‘gassho’ in Japan (and found widely throughout the world), the placing together of the palms of the hands in front of one’s face or upper chest (perhaps accompanied by bowing the head), is also typically recognized by Christians in the West as a posture of prayer. This does not mean that the meanings given to these gestures are exactly the same in each religion’s context.”
There is also a Jewish tradition dating back into antiquity and documented in the Talmud which relates to how the Babylonian Sage, Rabba (Abba ben Joseph, C. 280-352), used to pray with his hands folded.
Other religious historians say the gesture of praying with folded hands comes from the idea of a shackled prisoner’s hands which came to symbolize submission.
“Religious historians trace the gesture back to the act of shackling a prisoner’s hands with vine or rope: joined hands came to symbolize submission. In ancient Rome, a captured soldier could avoid immediate death by joining the hands together. Just as waving a white flag today, the message was clear. ‘I surrender.’ Centuries later, subjects demonstrated their loyalty and paid homage to their rulers by joining their hands. In time, clasping the hands together communicated both an acknowledgement of another’s authority and one’s own submission to that authority.”
As for Catholics, the Caeremoniale Episcoporum (1985) specifically addresses the correct Catholic posture concerning the folding of the hands during Mass and prayer: “When it says with hands folded, it is to be understood in this way: palms extended and joined together in front of the breast, with the right thumb over the left in the form of a cross” (#107, n.80)”.
It would not be accurate to say that the folding of the hands in prayer belongs any more to the Hindu religion than it does to various other world religions.