Standing Straight with Calmness after Ruku` (Ahadith 765-767)

Abu Humaid said: The Prophet (SAW) rose (from bowing) and stood straight till all the vertebra of his spinal column came to a natural position. [Taken from Chapter 127, volume 1 of the 9-volume version of Bukhari, translated by Muhsin Khan and published by Darussalam]
Volume 1, Book 12, Number 765:
Narrated Thabit:
Anas used to demonstrate to us the prayer of the Prophet and while demonstrating, he used to raise his head from bowing and stand so long that we would say that he had forgotten (the prostration).

Volume 1, Book 12, Number 766:
Narrated Al-Bara':
The bowing, the prostrations, the period of standing after bowing and the interval between the two prostrations of the Prophet used to be equal in duration.

Volume 1, Book 12, Number 767:
Narrated Aiyub:
Abu Qilaba said, "Malik bin Huwairith used to demonstrate to us the prayer of the Prophet at times other than that of the compulsory prayers. So (once) he stood up for prayer and performed a perfect Qiyam (standing and reciting from the Holy Qur'an) and then bowed and performed bowing perfectly; then he raised his head and stood straight for a while." Abu Qilaba added, "Malik bin Huwairith in that demonstration prayed like this Sheikh of ours, Abu Yazid." Abu Yazid used to sit (for a while) on raising his head from the second prostration before getting up.

In simple words, namaz mein takrein maarney se parhez kerein.
Give time to your body to settle after each change in position. It's really important if you wish to bring khushoo` to your Salah.

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