Reference: Majmoo’ Fataawa wa Rasaa.il Muhammad ibn Saalih al-‘Uthaymeen – Volume 13, Fatwa No.369
Question: Is there any mention in the Sunnah of the moment [when one should] stand for the prayer when the iqaamah is called?
Response: There is no mention in the Sunnah as to the moment [when one should] stand, other than the Prophet (sal-Allaahu ‘alayhi wa sallam) said:
«Do not stand [up for the prayer] until you see me», [Saheeh al-Bukhaaree, Hadeeth No.637 and Saheeh Muslim, Hadeeth No.156]
…so when the person stands [for the prayer] at the beginning of the iqaamah or during it or after it has finished, then all of that is permissible.