Al-Kāfi - Volume 5 > The Time for Compulsory Head Scarf
Hadith #2

2- مُحَمَّدُ بْنُ إِسْمَاعِيلَ عَنِ الْفَضْلِ بْنِ شَاذَانَ وَأَبُو عَلِيٍّ الأشْعَرِيُّ عَنْ مُحَمَّدِ بْنِ عَبْدِ الْجَبَّارِ عَنْ صَفْوَانَ بْنِ يَحْيَى عَنْ عَبْدِ الرَّحْمَنِ بْنِ الْحَجَّاجِ قَالَ سَأَلْتُ أَبَا إِبْرَاهِيمَ (عَلَيْهِ السَّلام) عَنِ الْجَارِيَةِ الَّتِي لَمْ تُدْرِكْ مَتَى يَنْبَغِي لَهَا أَنْ تُغَطِّيَ رَأْسَهَا مِمَّنْ لَيْسَ بَيْنَهَا وَبَيْنَهُ مَحْرَمٌ وَمَتَى يَجِبُ عَلَيْهَا أَنْ تُقَنِّعَ رَأْسَهَا لِلصَّلاةِ قَالَ لا تُغَطِّي رَأْسَهَا حَتَّى تَحْرُمَ عَلَيْهَا الصَّلاةُ.

2. Muhammad ibn ‘Isma’il has narrated from al-Fadl ibn Shadhan from and abu Ali al-Ash’ariy has narrated from Muhammad ibn ‘Abd al-Jabbar from Safwan ibn Yahya from ‘Abd al-Rahman ibn al-Hajjaj who has said the following: “I once asked abu Ibrahim, ‘Alayhi al-Salam, about the case of a girl who has not gained feeling of carnal desire, when must she use a veil to cover her head from non-relatives and when is it necessary to cover her head for Salat (prayer)? He (the Imam) said, ‘It is not necessary for her to cover her head until Salat (prayer) becomes obligatory on her.’”