Ya'la bin Mamlak asked Umm Salamah (may Allah be pleased with her) about the recitation and night prayer of the Prophet (peace and blessings be upon him). She said: "What have you to do with his prayer and recitation? He (peace and blessings be upon him) would pray, then sleep for as long as he had prayed, then pray for as long as he had slept, then sleep for as long as he had prayed, until morning came." Umm Salamah (may Allah be pleased with her) described his (peace and blessings be upon him) manner of recitation: the recitation of the Messenger of Allah (peace and blessings be upon him) was letter by letter (that is, every single letter could be understood).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4713