Sahih al-Bukhari, Volume 1, Book 8, Hadith 404 (USC-MSA) ⓘ
Narrated Anas: The Prophet said, "None of you should spit in front or on his right but he could spit either on his left or under his foot."
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 " .
also referenced under: Book 8, Hadith 62 (In-Book) & Hadith 412 (DarusSalam)