And you shall keep the Feast of Shavu'oth unto Yahuah Elohayka with a tribute of a freewill offering of your hand, which you shall give unto Yahuah Elohayka, according as Yahuah Elohayka has blessed you: And you shall rejoice before Yahuah Elohayka, you, and your son, and your daughter, and your manservant, and your maidservant, and the Leviyiy that is within your gates, and the stranger, and the fatherless, and the widow, that are among you, in the place which Yahuah Elohayka has chosen to place his name there.
Devariym (Deuteronomy) 16:10-11

For this reason it is ordained and written on the heavenly tablets, that they should celebrate the Feast of Shavu'oth in this month once a year, to renew the covenant every year.
Yovheliym (Jubilees) 6:17

And when the day of Shavu'oth was fully come, they were all with one accord in one place. And suddenly there came a sound from heaven as of a rushing mighty wind, and it filled all the house where they were sitting. And there appeared unto them cloven tongues like as of fire, and it sat upon each of them. And they were all filled with the Ruach Ha'Qodesh, and began to speak with other tongues, as the Ruach gave them utterance. 
Ma'asiym (Acts) 2:1-4