This day is called spy Sunday because Judas betrays Jesus in Matthew 26:6-16:
Jesus Anointed at Bethany
6 While Jesus was in Bethany in the home of Simon the Leper, 7 a woman came to him with an alabaster jar of very expensive perfume, which she poured on his head as he was reclining at the table.
“What are you willing to give me if I deliver him over to you?” So they counted out for him thirty pieces of silver.
matthew 26:15
8 When the disciples saw this, they were indignant. “Why this waste?” they asked. 9 “This perfume could have been sold at a high price and the money given to the poor.”
10 Aware of this, Jesus said to them, “Why are you bothering this woman? She has done a beautiful thing to me. 11 The poor you will always have with you,[a] but you will not always have me. 12 When she poured this perfume on my body, she did it to prepare me for burial. 13 Truly I tell you, wherever this gospel is preached throughout the world, what she has done will also be told, in memory of her.”
Judas Agrees to Betray Jesus
14 Then one of the Twelve—the one called Judas Iscariot—went to the chief priests 15 and asked, “What are you willing to give me if I deliver him over to you?” So they counted out for him thirty pieces of silver. 16 From then on Judas watched for an opportunity to hand him over.