Matthew 14:26
When the disciples saw Him walking on the water they became frightened, saying, "It is a spirit!" and cried out with fear.
Luke 24:37-39
But they became frightened and [even] terrified, and assumed they were seeing a spirit.
Hebrews 1:7
But God said [this] about the angels [Psa. 104:4 LXX], "He [i.e., God] makes His angels to be [like] winds and His servants [like] flames of fire." [Note: The idea is probably that angels obediently serve God's purpose similar to the way wind and lightening do].
Hebrews 1:14
Are not all angels ministering spirits sent out [by God] to serve those people who will inherit salvation?