A.T. Robertson Commentary John 11:13

"Now Jesus had spoken of his death: but they thought that he spake of taking rest in sleep." — John 11:13 (ASV)

Had spoken (ειρηκε). Past perfect of ειπον (ερω). The disciples had misunderstood Christ's metaphor for death.

That he spake (οτ λεγε). Present active indicative retained in indirect discourse after the secondary tense (εδοξαν).

Of taking rest in sleep (περ της κοιμησεως του υπου). Only use of κοιμησις (from κοιμαω) in the N.T., but it also was used of death . Hυπνου (in sleep) is objective genitive of υπνος (sleep, Matthew 1:24).