Although the hands clasped, or folded, is the most common Christian prayer position in modern culture, it hasn’t always been that way, nor is it universal. In some churches it is very common for people to pray with their arms raised and/ or palms outstretched.
I don’t know why the closed hands became prevalent. My WAG is that it stems from the story in the NT where Jesus denounced the man who prayed loudly in public – but I don’t know how the tradition came about.
Among Orthodox Christians, praying with the hands open and raised is quite common among those from the Middle East. As there is iconography predating Islam showing people in the orans posture (the proper name for it), it is probably a regional thing rather than an Islamic thing.
WAG, but I would venture that the preferred posture for prayer would depend upon whatever a particular culture deemed a properly reverential pose of supplication.