Imam Ahmad Ar-Raqee said:

Abu ‘Abdullah was asked, while I was present: What does it mean to put the right hand on the left hand during Salah?

So he said: Humbleness [and Humility] between the Hands of Allah (Exalted is He). [1]


[1] Tabaqat al-Hanabilah (1/84)

قال أحمد الرقي: سئل أبو عبد الله, وأنا حاضر: ما معنى وضع اليمين على الشمال في الصلاة؟ فقال: ذل بين يدي الله عز وجل