Sayyiduna Buraydah (may Allah be pleased with him) says that the Prophet (peace and blessings be upon him) said: "Between every two calls (i.e. the adhan and the iqamah) a (voluntary) prayer is to be offered, except for the Maghrib prayer."
Al-Bazzar recorded it; its chain contains Hayyan bin Ubaydullah, whom Ibn Adi mentioned, and according to one view he became confused (ikhtilat) in his narration.