Marroozi (rahimahullah) mentions:

I once saw Abu ‘Abdillah, Imaam Ahmed bin Hambal (rahimahullah), stand to complete his ma’mool (apportioned amount) of tahajjud after approximately half the night had passed. He then remained engaged in completing it until it was close to the time of sehri. I also saw him performing nafl salaah (i.e. the sunnah of awwaabeen) between maghrib and ‘esha.

(Siyar A’laam min Nubalaa vol. 11 pg. 223)