Reference: Siyar A’laam an-Nubalaa. – Volume 5, Page 296
Ibn Shubrumah said:
Zubayd used to divide the night into three parts:
i) a part for himself;
ii) a part for his son;
iii) and a part for his other son ‘Abdur-Rahmaan.
So he would pray [his third of the night], and then say to one of them:
‘Wake up’, and if he was lazy, he would pray his [third] part [of the night]. Then he would say to the other one:
‘Wake up’, and if he too was lazy, he would pray his [third] part [of the night].
So he would [end up] standing the entire night in prayer.