Sahih Muslim Book 004, Hadith Number 1175.
Chapter : It is forbidden to cry out for finding out the lost thing in the mosque.
'Abdullah (b. Mas'ud) reported: The Apostle of Allah (may peace be upon him) said five rak'ahs of the noon prayer and when he completed the prayer, It was said to him: Has there been (commanded) an addition In prayer? He said: What is it? They said: You have said five rak'ahs, so he performed two prostrations.