Bukhari

Hadith Commentary:
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Imam Bukhari rahimahullah has mentioned in the chapter heading the prohibition of spitting to the right side while in prayer, whereas the narrations are absolute (mutlaq); they do not specify the condition of prayer. However, in other narrations, the condition of prayer is present.
As is found in Sahih Bukhari, the hadith of Anas 413 and the hadith of Abu Hurairah radi Allahu anhu 416, therefore, according to Imam Bukhari rahimahullah, these absolute narrations will be interpreted in light of the restricted (muqayyad) narrations.
Is it permissible to spit to the right side outside of prayer or not? For this, other narrations must be consulted.

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Imam Nawawi rahimahullah has mentioned an absolute prohibition regarding this, whether one is in the mosque or outside the mosque, in prayer or outside of prayer.
Thus, the prohibition has been transmitted from numerous predecessors (salaf).
As is narrated from Abdullah ibn Mas'ud radi Allahu anhu that he declared spitting to the right side to be prohibited even outside of prayer. Mu'adh ibn Jabal radi Allahu anhu says, "Even after accepting Islam, I have never spat to the right side."
Umar ibn Abdul Aziz rahimahullah absolutely forbade his son from spitting to the right side.
Those who restrict the prohibition to the state of prayer, their evidence is probably the narration in which it is mentioned that during prayer, there is an angel on the right side.
(Sahih al-Bukhari, Kitab al-Salat, Hadith: 416)
This would be the case if, besides the angels who watch over and record good deeds, another angel is meant, because the watchers and the noble scribes (kiraman katibin) are always present on the right side.
(Fath al-Bari: 1/661)
Imam Bukhari rahimahullah, by adding the words "in prayer" (fi al-salat) in the chapter heading, has supported Imam Malik rahimahullah, because according to him, this prohibition is specific to prayer.
According to us, the position of Imam Bukhari rahimahullah is the preferred one, because during prayer, Allah ta'ala appoints an angel on the right side of the worshipper who protects his heart; therefore, during prayer, spitting to the right side is prohibited and to the left side is permissible.
It should be noted that the worshipper is permitted to spit to the left side only when there is no worshipper on his left, as we will clarify in the upcoming hadith. It is well-known regarding the permissibility of spitting to the left that the Shaytan is on the left side, who casts whispers into the heart; this spit falls on the head of Shaytan and thus becomes a means of his humiliation and disgrace.
The basis of this explanation is a narration which, although famous, is actually very weak. See:
Al-Mu'jam al-Kabir by al-Tabarani rahimahullah 8/199, Hadith number: 7808, second edition.