Sahih al-Bukhari 1215
Sahih al-Bukhari · Book 21: Actions while Praying · If a person in Salat is asked to step forward, or to wait, there will be no harm therein
Narrated Sahl bin Sa`d:
حَدَّثَنَا مُحَمَّدُ بْنُ كَثِيرٍ ، أَخْبَرَنَا سُفْيَانُ ، عَنْ أَبِي حَازِمٍ ، عَنْ سَهْلِ بْنِ سَعْدٍ ـ رضى الله عنه ـ قَالَ كَانَ النَّاسُ يُصَلُّونَ مَعَ النَّبِيِّ صلى الله عليه وسلم وَهُمْ عَاقِدُو أُزْرِهِمْ مِنَ الصِّغَرِ عَلَى رِقَابِهِمْ، فَقِيلَ لِلنِّسَاءِ " لاَ تَرْفَعْنَ رُءُوسَكُنَّ حَتَّى يَسْتَوِيَ الرِّجَالُ جُلُوسًا " .
The people used to offer the prayer with the Prophet (ﷺ) with their waist-sheets tied round their necks because of the shortness of the sheets and the women were ordered not to lift their heads till the men had sat straight.