﴿ ٱلَّذِينَ يُقِيمُونَ ٱلصَّلَوٰةَ وَيُؤْتُونَ ٱلزَّكَوٰةَ وَهُم بِٱلْءَاخِرَةِ هُمْ يُوقِنُونَ ﴾

“who are constant in prayer and spend in charity: for it is they, they who in their innermost are certain of the life to come!”

those who observe prayer performing it in the way that it should be performed and give alms and who are certain of the Hereafter knowing it to be true through the many proofs thereof hum ‘they’ is repeated because a separation has taken place between it the first hum and the predicate yūqinūna.