Midrasch zu Divrej Hajamim I 29:20

R. Joshua the son of Nehemiah said: The third was always the most precious. Adam had three sons, Cain, Abel, and Seth; and Seth was the most beloved, as it is said: This is the book of the generations of Adam, and that is followed by the sentence And begot a son in his own likeness (Gen. 5:3). Noah had three sons, as it is said: And Noah begot three sons: Shem, Ham, and Japheth (ibid. 6:10), and though Japheth was the eldest, only Shem merited greatness. Amram had three children, Miriam, Aaron, and Moses, and it is written: Had not Moses His chosen stood before him (Ps. 106:23). Concerning the tribes of Reuben, Simeon and Levi, Levi was the most important, as it is said: At that time the Lord separated the tribe of Levi (Deut. 10:8). Among the kings Saul, David, and Solomon, Solomon was the most beloved, as it is said: Solomon sat on the throne of the Lord (I Chron. 29:23). In the case of months, the third month is the most precious, as it is stated: In the third month (the Torah was given).