Sayyiduna Ali (may Allah be pleased with him) narrates that there was a specific time during the pre-dawn meal (sahri) when I would present myself in the service of the Prophet (peace and blessings be upon him). If the Prophet (peace and blessings be upon him) was standing and performing prayer at that time, he would say "Subhan Allah," which was a sign that I was permitted to enter. And if he was not performing prayer at that time, he would simply grant permission (and there would be no need to say "Subhan Allah").