Reference for Bava Batra 6:2
וניעבדו תלתין אמין בבנין ואידך ניעביד פרוכת כי קאי תלתין אמהתא נמי אגב תקרה ומעזיבה הוה קאי בלא תקרה ומעזיבה לא הוה קאי
Why did they not [in the Second Temple] build a wall thirty cubits high and use a curtain for the remaining [seventy cubits]? — Even the thirty cubit wall [of the First Temple] was only sustained by the ceiling and plaster [of the room above it], but without such a ceiling and plaster it could not stand [with a breadth of only six handbreadths]. But why did they not build a wall as high as possible [with a breadth of six handbreadths] and use a curtain for the rest? — Abaye replied: It was known to them by tradition that the partition should be wholly a wall or wholly a curtain, either wholly a wall as in the First Temple, or wholly a curtain as in the Tabernacle.