After Ibn Ishaq, there are a number of shorter accounts (some of which are earlier than Ibn Ishaq) recorded in different forms (see List of earliest writers of sīra). Other biographies of Muhammad include al-Waqidi's (d. 822) and then Ibn Sa'd's (d.844–45). Al-Waqidi is often criticized by early Muslim historians who state that the author is unreliable. These are not "biographies" in the modern sense of the word, but rather accounts of Muhammad's military expeditions, his sayings, the reasons for and interpretations of verses in the Quran.