‘Abdullah (rahimahullah), the son of Imaam Ahmad (rahimahullah), narrates the following:

My father would perform three hundred rakaats of Nafl Salaah every day. When he became weak, due to the lashes which were meted to him as punishment (from the side of the king for standing against the deviated sect of his time) he would perform 150 rakaats daily. At that time, he was nearly eighty years old.

He would recite one seventh of the Qur’aan Majeed every day and would thus complete the recitation of the Qur’aan Majeed every seven days. He would complete the recitation of the Qur’aan Majeed in Tahajjud Salaah every seven nights, and this khatam was separate to the khatam which he would make in his Nafl Salaah during the day. After performing the Esha Salaah, he would nap for a short while after which he would awaken and engage in performing Tahajjud Salaah and making du‘aa.

(Manaaqib Imaam Ahmad libnil Jowzi pg. 382)