The use of "werden" instead of "sein" as the passive auxiliary is a relatively recent phenomenon, unknown, for example, in Middle High German. It did not become firmly established until the 16th century, and even then mostly in the South. We still find - admittedly old-fashioned - examples of "sein:" "Er wollte nicht erkannt sein" (He didn't want to be recognized). This is particularly true when authors want(ed) to avoid the awkwardness of long verb chains. Thus "dass [er] ... in die Verbannung geschickt sein mochte," instead of "geschickt worden sein mochte"¹

The use of "sein" instead of "werden" has stuck around in various set phrases, as with "gebären": "Ich bin im Krankenhaus geboren."

"Sein" is particularly prevalent in the passive imperative:
• Sei gegrüßt!
• Seien Sie gesegnet!
• Gott sei es gedankt!

In fact, "sein" is more common than "werden" in the passive imperative, although the latter appears in Luther's Bible: "Geheiligt werde dein Name."

Several other auxiliaries may be encountered in an unusual combination of the active and passive. The object of the action remains in the accusative, and the verb acting upon it becomes a past participle, but an active subject is introduced with a verb like "bekommen," "erhalten," "gehören," etc.:

• Ich habe das Geld überwiesen bekommen.
• Du bekommst das Geld von mir bezahlt.
• Mädchen bringen den Hut auf einer Stange getragen. [a quotation from Schiller's Wilhelm Tell]
• Sie nehmen ihn gefangen.
• Du gehörst ins Gefängnis geliefert.
• Jeder Student erhielt fünf Bücher zugezählt.