Seven days

Leviticus 23:36-42
For seven days you are to present an offering made by fire to the LORD. On the eighth day you are to hold a sacred assembly and present an offering made by fire to the LORD. It is a solemn assembly; you are not to do any regular work. . . .

Numbers 29:12-38
On the fifteenth day of the seventh month, you are to hold a sacred assembly; you must not do any regular work, and you shall observe a feast for the LORD for seven days. . . .

because

Deuteronomy 16:10
And you shall celebrate the Feast of Weeks to the LORD your God with a freewill offering that you give in proportion to how the LORD your God has blessed you,

Deuteronomy 7:13
He will love you and bless you and multiply you. He will bless the fruit of your womb and the produce of your land--your grain, new wine, and oil--the young of your herds, and the newborn of your flocks, in the land that He swore to your fathers to give you.

Deuteronomy 28:8-12
The LORD will decree a blessing on your barns and on everything to which you put your hand; the LORD your God will bless you in the land He is giving you. . . .

Deuteronomy 30:16
For I am commanding you today to love the LORD your God, to walk in His ways, and to keep His commandments, statutes, and ordinances, so that you may live and increase, and the LORD your God may bless you in the land you are entering to possess.