"Keep my cheek on the ground..." the last words of Umar

Uthman ibn Affan  said:
I was the last to see Umar ibn al-Khattaibn I called upon him and saw his head on the lap of his son Abdullah, while he was weary. He told his son: "Keep my cheek on the ground." 
Abdullah refused, so he said: "Keep my cheek on the ground." 
Abdullah refused, so he said: "Keep my cheek on the ground, you motherless one." 
So he kept his (Umar's) cheek on the ground, and then Umar said: "O my mother! Woe to me, my mother! I am not forgiven (by Allah)." 
He went on saying that till he died.