Sayyiduna Rabi'ah bin Ka'b al-Aslami (may Allah be pleased with him) said: I used to sleep in the apartment of the Prophet (peace and blessings be upon him), and when he (peace and blessings be upon him) stood up at night to pray, I would hear him (peace and blessings be upon him) saying for a long while (al-hawi): "Alhamdu lillahi Rabbil-'alamin" (All praise is for Allah, Lord of the worlds), then saying for a long while (al-hawi): "Subhana Rabbiyal-'Azimi wa bihamdih" (Glory and praise be to my Lord, the Magnificent). I asked: What is meant by al-hawi? He said: "Supplicating for a while."
Hadith Referenceالمعجم الكبير للطبراني / باب الراء / 4554