XmCreateMessageDialog(3) on Linux
The text 1d9f6b61cdb6, as Debian 13 (Trixie), Debian 12 (Bookworm), Debian 11 (Bullseye), Debian 10 (Buster), Debian 9 (Stretch), Debian 8 (Jessie) shipped it.
The MessageBox MessageDialog convenience creation function "XmCreateMessageDialog" "creation functions" "XmCreateMessageDialog"