Tafsir of Al-Ma'aarij 70:23

That is: those who are persistent in performing them, not failing to do so, and not letting any distractions occupy them away from them. In this, there is an indication of the virtue of constancy in worship. Ibn Hibban recorded from Abu Salamah, who said: Aisha told me that the Messenger of Allah (may Allah Most High bless him and grant him peace) said: "Take upon yourselves such deeds as you are capable of, for Allah Most High does not tire until you tire." She said: "The most beloved of deeds to the Messenger of Allah (may Allah Most High bless him and grant him peace) was that which one persists upon, even if it be small. And when he performed a prayer, he would persist in it." Abu Salamah read: "Those who are persistent in their prayers." Ahmad also recorded in his Musnad from her that she said: "His deeds (may Allah Most High bless him and grant him peace) were consistent (dimah)." Jar Allah said: He did not perform any act of goodness without making it a habit, performing it whenever its time arrived. This is interpreted to mean that the act is a stable state upon which a person continues; then it is rendered as the state itself, which contains an evident hyperbole and indicates that it was a firm disposition (malakah) for him, peace and blessings be upon him.

It is also said that "persistent" (da'imun) means they do not turn away (their focus) during it—derived from the expression "standing water" (al-ma' al-da'im). This was narrated from Imran bin Husayn, and likewise from Uqbah bin Amir. Ibn al-Mundhir recorded from Abu al-Khayr that Uqbah asked them: "Who are 'those who are persistent in their prayers'?" We said: "Those who are always praying." He replied: "No, but rather those who, when they pray, do not turn to the right or to the left." Al-Zujaj held this view. Thus, the verse implies a condemnation of turning away [looking around] during prayer, and the Traditions have explicitly stated this. Some have inferred from this that it is a major sin; its verification is in al-Zawajir.

From Ibn Mas'ud and Masruq, it is said that persistence means performing them at their appointed times, though this is as you see [i.e., not the primary linguistic meaning]. Perhaps the refraining from turning away and the performing of them on time are both included in the term "guarding" (al-muhafazah) which follows later, if Allah Most High wills.

Regarding "the prayer," according to what 'Abd bin Humayd recorded from Ibrahim al-Taymi, it refers to the obligatory prayer. According to Imam Abu Ja'far (may Allah Most High be pleased with him), it refers to the supererogatory prayer. It is also said it refers to whatever they were commanded of it absolutely. Al-Hasan read it as salawatihim (plural).