Following is the hadith in musnad ahmed:
Sayyiduna Hulb (ra) relates, 'I saw the Prophet (sallallahu alaihi wa sallam) turn from both his right and left and I also saw him place this upon his chest.' Yahya (one of the narrators) described this as being the right hand upon the left above the wrist joint. (Ahmad 21460.)
Imam Nimawi comments in his al T'aleeq al Hasan (1/145):
'I have a suspicion that the wording of this hadeeth has mistakenly been changed by a writer. The correct words would appear to be "Yadhau hadhihi ala hadhihi", i.e., "he would place this hand upon this hand", and not "hadhihi ala sadrihi", i.e., "this hand upon his chest". Only this wording would be in agreement with the narrators own interpretation of the hadeeth as is stated in the narration "Yahya described this as being the right hand upon the left above the wrist joint". This would also tally with all the other narrations of this hadeeth that do not contain the wording "upon the chest".
I know that this is a matter of dispute but I only wanted to know whether imam nimawi's point is valid. Because the hadith wording is quite strange as it mentions only one hand i.e. "place this hand on chest". I just want answer to this for knowledge I know this matter is broad in scope.