The Imam narrates the aforementioned words "Subhan Allah" and "clearing the throat" from his teachers, Yusuf bin Musa, Al-Durqi, and Muhammad bin Yahya, through their chains of narration.
Hadith Referenceصحيح ابن خزيمه / جماع أبواب الأفعال المباحة فى الصلاة / 904