When is reciting aloud (Jahr) preferred over secret recitation (Sirr) during Tahajjud?
Chapter on the Times When Prayer is Prohibited
Al-Mughni
Book of Prayer
Primary text
Reciting aloud is preferred if it makes the reciter more energetic or if someone nearby can listen and benefit from the recitation. This is supported by the incident where the Prophet instructed Abu Bakr, who was reciting quietly, to raise his voice slightly, while telling Umar, who was reciting loudly, to lower his voice somewhat.
Supporting text
Reciting secretly is superior if someone nearby is also engaged in Tahajjud or if raising the voice would cause harm or disturbance to another worshipper. If neither of these conditions applies, the worshipper may choose whichever method they wish.