The men used to pray with the Prophet ﷺ with their Izars tied around their necks as boys used to do; therefore the Prophet ﷺ told the women not to raise their heads till the men sat down straight (while praying).  

كَانَ رِجَالٌ يُصَلُّونَ مَعَ النَّبِيِّ ﷺ عَاقِدِي أُزْرِهِمْ عَلَى أَعْنَاقِهِمْ كَهَيْئَةِ الصِّبْيَانِ وَقَالَ لِلنِّسَاءِ لاَ تَرْفَعْنَ رُءُوسَكُنَّ حَتَّى يَسْتَوِيَ الرِّجَالُ جُلُوسًا