His saying: "Have they not considered what things Allah has created, whose shadows turn" means: they return. "His shadows" refers to the shadow of everything. "From the right and the left" – the interpretation of al-Hasan is: the shade is sometimes on the right and sometimes on the left. "Prostrating to Allah while they are dakhirun" means: humbled.
Muhammad said: It is said: dakhira li-Allah, meaning: he submitted. And "sujjadan" (prostrating) is in the accusative case as a circumstantial qualifier (hal).