Bechorot 5a
A Roman general Controcos(8) questioned R. Johanan b. Zakkai.
‘In the detailed record of the numbering of the Levi'im, you find the total is twenty-two thousand three hundred,(9) whereas in the sum total you only find twenty-two thousand.(10) Where are the [remaining] three hundred?’
He replied to him:
[‘The remaining] three hundred were [Levite] first-born, and a first born cannot cancel the holiness of a first-born’.
What is the reason?
said Abaye: Because it is sufficient for a [Levite] first-born to cancel his own holiness.
(8) Rashi and Tosaf. in Hullin 27b read Contricon. There are a number of variants in the reading of this name, owing to corruptions. It is suggested that the name refers either to Quintus or Quietus. V. Hul., Sonc. ed., p. 141, n. 2.
(9) The families of Gershom numbered seven thousand and five hundred, the families of Kohat numbered eight thousand and six hundred, and the families of Merari numbered six thousand and two hundred, making a grand total of the families of the Levi'im of twenty-two thousand and three hundred.
(10) V. BaMidbar 3:39.