Ausbund is the oldest Protestant hymnal. First edition — 1564. Still used. Every Sunday.
Origin
Written by Anabaptists in prison at Passau Castle (Bavaria), 1535-1540. 51 hymns. Authors were imprisoned for their faith. Many were later executed. The hymns are their testament. Later expanded to 140 hymns.
How They Sing
Without instruments (musical instruments = vanity). Without sheet music (transmitted orally). One voice begins, others join. Very slowly (one syllable = 4-8 seconds). A 4-verse hymn can last 20 minutes. Sounds like Gregorian chant.
Language
16th-century High German. Many Amish don't understand every word — but know them by heart. Melodies (Weisen) aren't written — passed from father to son for 460 consecutive years.
Lob Lied
Second hymn at every Sunday service — always 'O Gott Vater, wir loben dich' (Lob Lied). Sung in every Amish community worldwide. Every Sunday. For 460 years. This may be the longest continuously performed song in human history.