Sahih al-Bukhari
Sahih al-Bukhari 412
It is forbidden to spit on the right side while in Salat (prayers)
Arabic hadith text
حَدَّثَنَا حَفْصُ بْنُ عُمَرَ، قَالَ حَدَّثَنَا شُعْبَةُ، قَالَ أَخْبَرَنِي قَتَادَةُ، قَالَ سَمِعْتُ أَنَسًا، قَالَ قَالَ النَّبِيُّ صلى الله عليه وسلم "لاَ يَتْفِلَنَّ أَحَدُكُمْ بَيْنَ يَدَيْهِ وَلاَ عَنْ يَمِينِهِ، وَلَكِنْ عَنْ يَسَارِهِ أَوْ تَحْتَ رِجْلِهِ "
Translation
Narrated Anas
The Prophet (ﷺ) said, "None of you should spit in front or on his right but he could spit either on his left or under his foot."