Lady Aisha (may Allah be pleased with her) said: The wives of the Messenger of Allah (peace and blessings be upon him) used to pray the Fajr prayer with the Prophet (peace and blessings be upon him), then they would return wrapped in their cloaks before they could be recognized.
Hadith Referenceسنن دارمي / من كتاب الصللاة / 1250
(Commentary on Hadith 1249) That is, the Messenger of Allah (sallallahu alayhi wa sallam) would perform the Fajr prayer so early that even upon returning, due to the darkness, the women could not be recognized.