(Imām Bukhārī narrates): Mu'alla bin Asad narrated to us, he said: Wuhaib narrated to us, from Abdullah bin Tawus, from his father, from Hazrat Ibn Abbas (may Allāh be pleased with both of them), he said that
a menstruating woman has been given the concession that when her menses begin, she may set out with the caravan.
حَدَّثَنَا مُعَلَّى بْنُ أَسَدٍ، قَالَ حَدَّثَنَا وُهَيْبٌ، عَنْ عَبْدِ اللَّهِ بْنِ طَاوُسٍ، عَنْ أَبِيهِ، عَنِ ابْنِ عَبَّاسٍ
قَالَ رُخِّصَ لِلْحَائِضِ أَنْ تَنْفِرَ إِذَا حَاضَتْ وَكَانَ ابْنُ عُمَرَ يَقُولُ فِي أَوَّلِ أَمْرِهِ إِنَّهَا لاَ تَنْفِرُ، ثُمَّ سَمِعْتُهُ يَقولُ تَنْفِرُ، إِنَّ رَسُولَ اللَّهِ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ رَخَّصَ لَهُنَّ
Reference: Sahih Al Bukhari 329