Unus ex disciplulis meis...

The 3rd responsorium in the 2nd nocturn of Matins, the third sung at Tenebrae, of Maundy Thursday.

Unus ex discipulis meis tradet me hodie: vae illi per quem tradar ego: melius illi erat, si natus non fuisset. 

One of my disciples will this day betray me: woe to him by whom I am betrayed: it had been better for him if he had never been born.