The Messenger of Allah ﷺ used to place his right hand over his left and clasp them together on his chest while in prayer.
حدثنا أبو توبة حدثنا الهيثم يعني ابن حميد عن ثور عن سليمان بن موسى
كان رسول الله ﷺ يضع يده اليمنى على يده اليسرى ثم يشد بينهما على صدره وهو في الصلاة
No references are available.
[Sahih]. It is found in Al-Marasil by Abu Dawud, no. 33, and its chain is daif due to its being a mursal narration. The hadith has a corroborating witness in Ahmad, 5/226, and its chain is hasan, and by this the hadith is confirmed as sahih.