Should a worshiper recite aloud or silently if another person joins him in a supererogatory prayer?

There is no objection, according to some scholars like the Shafi'is, to a person performing an obligatory prayer following one performing a supererogatory prayer. They cite as evidence the hadith of Mu'adh ibn Jabal (may Allah be pleased with him) that he used to pray 'Isha with the Prophet (peace and blessings be upon him), and then lead his companions in prayer. Recitation is audible in supererogatory night prayers and inaudible in supererogatory day prayers.