After having repeatedly examined my conscience before God, I have come to the certainty that my strengths due to an advanced age are no longer suited to an adequate exercise of the Petrine ministry. In order to govern the bark of St. Peter and proclaim the Gospel, both strength of mind and body are necessary — strengths which in the last few months, have deteriorated in me to the extent that I have had to recognize my incapacity to adequately fulfill the ministry entrusted to me.

Statement announcing his resignation as pope, quoted in ABCNews, 'Pope Benedict to Resign, Vatican Says' (11 February 2013)