Umar bin Khattab reported,
I do not know it except that he traced it back to the Prophet, who said, "Allah 
says, 'Whoever humbles himself before Me like this,'" and Yazid placed the inside of his palm toward the ground and brought it close to the ground, "'I will raise him like this,'" and he turned the inside of his palm toward the sky and lifted it upward.
Ahmad 309
Sahihحدثنا يزيد أنبأنا عاصم بن محمد عن أبيه عن ابن عمر
عن عمر رضي الله عنه قال
لا أعلمه إلا رفعه قال يقول الله تبارك وتعالى من تواضع لي هكذا وجعل يزيد باطن كفه إلى الأرض وأدناها إلى الأرض رفعته هكذا وجعل باطن كفه إلى السماء ورفعها نحو السماء
Its chain of transmission is sahih. Asim is the son of Muhammad bin Zayd bin Abdullah bin Umar. His father Muhammad heard from his grandfather Abdullah bin Umar. The hadith is found in Majma al-Zawaid 8:82, attributed to Ahmad and Bazzar, where it states, "The narrators of Ahmad and Bazzar are the narrators of the sahih." In H there is an addition raising this, placed right after his saying "whoever humbles himself for me thus" and before Ahmad's statement, "and Yazid put the palm of his hand toward the ground." This is an addition out of place, and it is not found in K, nor in H, nor in Majma al-Zawaid, so we removed it.