Avengers #160

In the June 1977 issue, the Grim Reaper KOs the Scarlet Witch, along with some of her comrades-in-arms, with a blast from his scythe, and holds them in quasi-bondage with some energy-induction bands placed upon their wrists. When the interrogation session doesn't go the way he envisioned, he knocks them unconscious again.
Source: My Collection