Is it permissible to consistently perform the jalsat al-istiraahah (resting sitting) in every prayer, and when did the Prophet (peace and blessings be upon him) perform it in his life?

The Prophet, peace and blessings be upon him, sometimes performed the sitting of istirāḥah (a short rest after the prostration of the first and third rakʿah) and sometimes omitted it. It has not been established that he performed it during a specific period of his life to the exclusion of others. Ibn Ḥajar refuted those who argued against its recommendability by claiming that the Prophet, peace and blessings be upon him, performed it in his old age, stating that such an interpretation requires proof. The ḥadīth "Pray as you have seen me pray" is an evidence for emulating him.