Is it permissible to pray two Rak'ahs after 'Ishā' with the intention of praising [Allah]?

Praying two rak'ahs with the intention of praising Allah (what some people call 'Salat al-Shukr' or 'Prayer of Gratitude') is not based on any legal Islamic evidence. The 'Prayer of Gratitude' (Salat al-Shukr) does not exist in Islamic law. What does exist is 'Sujud al-Shukr' (Prostration of Gratitude) when a new blessing is received. If a Muslim prays two rak'ahs at any time with the intention of thanking and praising Allah, this is a good deed, but without specifically calling it 'Salat al-Shukr'. Furthermore, committing to two rak'ahs after the 'Isha prayer with the intention of praise is considered an additive innovation (bid'ah idafiyyah), and the one who performs it should be advised accordingly.