سَاهُونَ (heedless): Inattentive of their prayer, delay it from its time.

Those who just perform the outer acts of the prayer without applying its meaning and essence. Allah (swt) says:

     ﴾إِنَّ الصَّلَاةَ تَنْهَىٰ عَنِ الْفَحْشَاءِ وَالْمُنكَرِ﴿

 (Indeed, prayer prohibits immorality and wrongdoing,)
(Al-Ankaboot: 45)

It is a great mercy of Allah (swt) towards His Servants that He (swt) made the woe for those who are heedless of their prayer, not heedless during their prayer. That is why when a Bedouin heard this verse said: All praise is due to Allah (swt) that He said: (of their prayer) and did not say: (during their prayer) because all of us may be subjected to  heedless in our prayer, even the devout people and those who establish the prayer rightfully.