Je was op zoek naar: affirming (Engels - Swahili)

(they keep affirming their) obedience and saying good words.
ut'iifu na kauli njema.

but then their affirming served them nothing after they had seen our torment.
lakini imani yao haikuwa yenye kuwafaa kitu wakati ambao wamekwisha iona adhabu yetu.

when a messenger was sent to them by god affirming the books they had already received, some of them put (his message) behind their backs as if they had no knowledge of it.
na alipo wajia mtume kutoka kwa mwenyezi mungu, mwenye kuthibitisha yale waliyo nayo, kundi moja miongoni mwa wale walio pewa kitabu lilitupa kitabu cha mwenyezi mungu hicho nyuma ya migongo yao kama kwamba hawajui.

and this (qur'an) is another book that we have revealed, blessed, affirming the earlier (revelations), so that you may warn the people of (makkah) the town of towns, and those who live around it.
na hiki ni kitabu tulicho kiteremsha, kilicho barikiwa, chenye kuhakikisha yaliyo tangulia, na ili uuwonye mama wa miji na walio pembezoni mwake.