Does ostentation (riya') fall under the angels' awareness of a servant's deeds?

Riya' (showing off) is when a servant intends for their action to be for other than Allah, not merely the awareness of created beings. The guardian angels record the deeds of servants, and nothing can be hidden from them. Therefore, thinking that the angels' awareness constitutes riya' is a whisper from Satan to deter one from worship. One must not pay attention to these whispers and should proceed with worship sincerely, both in secret and openly. Abandoning an action out of fear of riya' is not sincerity; rather, sincerity is performing acts of obedience purely for Allah Almighty.