Marzolph, Ulrich. Arabian Nights. Kate Fleet; Gudrun Krämer; Denis Matringe; John Nawas; Everett Rowson (编). Encyclopaedia of Islam 3rd. 2007. doi:10.1163/1573-3912_ei3_COM_0021. Arabian Nights, the work known in Arabic as Alf layla wa-layla
Levias, Caspar. Numbers and numerals. Singer, Isidore; et al (编). Jewish Encyclopedia 9. New York: Funk & Wagnalls Company: 349. 1905. "Forty: Stands in the Bible for a generation (e.g., the forty years of wandering in the desert), hence for any period of time the exact duration of which is unknown (comp. Gen. vii. 4, 12, 17; viii. 6; Ex. xxiv. 18, xxxiv. 28; Deut. ix. 9, 11, 18; x. 10; I Sam. xvii. 16; I Kings xix. 8; Jonah iii. 4). In later literature forty is commonly used as a round number (comp. Giṭ. 39b, 40a; Soṭah 34a; Yer. Ta'an. iv. 8; et al.)."
