at.

1 Corinthians 15:32
If I fought wild beasts in Ephesus for human motives, what did I gain? If the dead are not raised, "Let us eat and drink, for tomorrow we die."

Pentecost.

Exodus 23:16
You are also to observe the Feast of Harvest with the firstfruits of the produce from what you sow in the field. And observe the Feast of Ingathering at the end of the year, when you gather your produce from the field.

Leviticus 23:15-21
From the day after the Sabbath, the day you brought the sheaf of the wave offering, you are to count seven full weeks. . . .

Acts 2:1
When the day of Pentecost came, the believers were all together in one place.