Imam Ahmad b. Hanbal: Soul of Deceased Returns to Its Body in Grave

One of the errors of Imam Ahmad b. Hanbal was his belief that the spirit of the deceased returns to its body in the grave:
He said:

أَنَّهُ يَقْبِضُ الأَرْوَاحُ ثُمَّ تُرَدُّ في الأَجْسَادِ في القُبُورِ

(And we believe that) the Angel of Death takes the souls, then returns them to the bodies in the graves.

Source: Tabaqatul Hanabilah, vol. 2, p. 430