As Salam o Alaikum
Are there any specific ruling on the position of Ru'kuu while in Salah? I heard someone say that when you are in Ru'kuu your fingers should be straight, and not spread. And your palm should rest exactly upon your knee, and not above it...
JazakAllah

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

In Ruku’ (bowing), the head should be on the same level as the hips of a person and the hands should be supported by the knees while the arms should be apart from one’s sides, and the fingers should be spread apart upon the knees and legs, and the back should be straight (in an horizontal position). It is reported that ‘Uqbah ibn ‘Aamer “made Ruku’ while spreading his arms aside, and he put his hands on his knees and he opened his fingers beyond his knees and he said: “This is how I saw the Prophet pray.” [Ahmad, Abu Daawood and An-Nasaa’i] Also, An-Nasaa’i reported that when the Prophet made Ruku’, he would be level, his head neither up nor down (with respect to his hips). Moreover, ‘Ali said: “When the Prophet made Ruku’, if you were to put a cup of water on his back, its contents would not spell." [Ahmad] Besides, Abu Humayd As-Saa’idi narrated that when the Prophet made Ruku’, he would firmly put his hands on his knees while making his back straight (with respect to his hips). [Al-Bukhari]

Allaah Knows best.