صحيح ابن خزيمه
Sahih Ibn Khuzaymah
جماع أبواب الأفعال المباحة فى الصلاةChapters on Permissible Acts in Prayer
(329) بَابُ الدَّلِيلِ عَلَى أَنَّ إِبَاحَةَ بَزْقِ الْمُصَلِّي تَحْتَ قَدَمِهِ الْيُسْرَى329 Chapter: Evidence That Spitting under the Left Foot Is Permitted.
Hadith Q877
إِذَا لَمْ يَكُنْ عَنْ يَسَارِهِ فَارِغًا، وَإِبَاحَةِ دَلْكِ الْبُزَاقِ بِقَدَمِهِ إِذَا بَزَقَ فِي صَلَاتِهِ
When his left side is not empty, and when he spits during prayer, it is also permissible to rub it with his foot.
