Does the intention to end the prayer with the Tasleem, then delaying the Tasleem to supplicate immediately before it, invalidate the prayer?

The intention to say Tasleem after the Tashahhud and then abandoning it to increase in remembrance (dhikr) and supplication (du'a) does not invalidate the prayer. It is not like intending to break off the prayer. Al-'Izz ibn 'Abd al-Salam mentioned that this does not affect the validity of the prayer, and he gave examples, including the intention to shorten the prayer and then intending to lengthen it, and the intention to say Tasleem after the Tashahhud and then prolonging the supplications and remembrances.