From: Igbo, West Africa
Source: Igbo (Nigeria) proverb (Ugo chara acha adighi echu echu); explanation from lingalot.com's Igbo proverbs page, which translates it "A mature eagle feather will forever remain pure". Earlier recorded here as documented by Chinedu V. Onyema (Cataloging Africa); that source was not read.
The source explains it: someone who is well trained or well educated will stand the test of time
. The wording of the meaning is ours.