ٱلَّذِىٓ أَنقَضَ ظَهْرَكَ ٣
Sentence structure
ٱلَّذِىٓ describes وِزْرَكَ. أَنقَضَ forms its relative clause with understood subject هُوَ, and ظَهْرَكَ is the object.
Ayah summary
That burden had weighed heavily upon your back, O Prophet ﷺ.
ٱلَّذِىٓ — which
Grammar: A masculine-singular relative noun describing وِزْرَكَ.
أَنقَضَ — weighed upon
Grammar: A Form IV perfect in the relative clause with understood subject هُوَ.
ظَهْرَكَ — your back
Grammar: A masculine accusative object; attached كَ is possessor.