Sahih Muslim Book 004, Hadith Number 1168.
Chapter : It is forbidden to cry out for finding out the lost thing in the mosque.
'Alqama narrated It on the authority of 'Abdullah (b. Mas'ud) who said: The Messenger of Allah (may peace be upon him) said the prayer; (the narrator added): He made some act of omission or commission when he pronounced salutation; it was said to him: Messenger of Allah, is there something new about (he prayer? He (the Holy Prophet) said: What is it? They said: You said prayer in such and such away. He (the narrator) said: He (the Holy Prophet) turned his feet and faced the Qibla and performed two prostrations and then pronounced salutations, and then turned his face towards us and said: If there is anything new about prayer (new command from the Lord) I informed you of that. But I am a human being and I forget as you forget, so when I forget, remind me, and when any one of you is in doubt about his prayer, he should aim at what Is correct. and complete his prayer in that respect and then make two prostrations.