The Ruling on prolonging the Last Prostration
Question :
I observe that some Imams may Allah guide them - prolong the last prostration of the prayer; is this supported by the Islamic law? And is there any basis for changing the intonation of the voice in order to be known that this is the sitting of the Tashahhud?
Answer:
I know of no evidence to support prolonging the last prostration; it is only reported in the Hadiths that the prostrations are of equal or similar length. As for changing the intonation of the voice when pronouncing the Takbir of sitting, it is something which is well known and practised by the Imams, and it may be that their evidence is its continual practice passed down through the ages, since such a thing could not be transmitted through writing and is therefore dependent upon transmission (through practice). And the benefit of it is attained, and that is that the worshippers are informed that this is the sitting of Tashahhud, so that they do not stand up after the Takbir.
Source:
Ibn Jibreen
Fatawa Islamiyah, Vol. 2 Page 199