Which one of the following is not a primary source of Muslim Law?

In Islamic jurisprudence, the four primary (formal) sources of Muslim Law are the Quran, Sunna or Ahadis (Traditions of the Prophet), Ijma (consensus of jurists), and Qiyas (analogical deduction). Custom (Urf), along with judicial decisions, legislation, and justice, equity and good conscience, is classified as a secondary (extrinsic) source of Muslim Law rather than a primary source.