As the servant rises from the bowing position to stand upright once more, returning his body to its most fitting posture, it is prescribed that the slave exalt Allah to thank Him and praise Him for His bounties and for facilitating him and guiding him to experience this humility and submission that He prevented others from experiencing.
Just as the Qur’an is prescribed for the slave to recite while he was in the standing posture before bowing, Allah prescribed for His slave to praise Him and glorify Him, when he is standing erect after having risen from bowing. In fact, the effect of this pillar on the heart is unique; an effect that cannot be produced by anything except the act of the bowing that preceded it. It is an essential pillar similar to other pillars of salah such as bowing down and prostration. And for this reason the Messenger of Allah, peace and blessings of Allah be upon him, used to prolong this standing (after bowing) just as he prolonged the pillars of bowing and prostration, and he used to praise, glorify and extol Allah much therein, and exalt Him as I have mentioned before she I explained the description of his salah. He used to say in his night prayers (qiyam al-layl): “To my Lord be all praise, to my Lord be all praise.” repeating it until his standing was as long as his ruku.
Inner Dimensions of the Prayer by Ibn Qayyim Al-Jawziyyah Page 49