What is the ruling on saying "Ya Salati 'ala al-Nabi" (O my prayers be upon the Prophet) when expressing wonder or admiration, and is the "Ya" here for exclamation or supplication?

The saying "Ya Salat Al-Nabi" (O Prayer of the Prophet) when admiring something is permissible, though some scholars disliked it. Shirk (polytheism) occurs when supplicating to other than Allah for seeking benefit or repelling harm. If the one saying it does not intend seeking aid (istighatha), then there is no harm. The Sunnah when admiring something is to supplicate for blessing, not to send prayers upon the Prophet. However, sending prayers upon the Prophet in this context is permissible and not disliked.