WE RELATE FROM the book of Ibn as-Sunnī that Ibn ‘Abbās
related that when the Messenger of Allah
returned from a journey and went to his family he said: “Turning turning, to our Lord returning, not leaving behind any sin [unforgiven].” [1].
Tawban tawbā, li-Rabbinā awbā, lā yughādiru ḥawbā.
I say that tawban tawbā is asking for tawbah, ‘to turn towards’. It is in the accusative case either by being connected to the implicit [phrases] ‘turn to us’ (tub ‘alaynā tawbā) or ‘we ask You for repentance’ (nas’aluka tawbā). The word awbā is in the same sense and takes its meaning from the verb āba, meaning ‘he returned’. The phrase ‘not leaving’ means ‘not discarding’ and the word ḥawbā’, meaning ‘sin’ (ithm), and is written with a fatḥah on the ḥā’ or with a ḍammah (ḥūban).
References
[1] Ibn as-Sunnī (536). Ibn Ḥajar grades it as ṣaḥīḥ.