Azriel of Gerona, Perush ‘Eser Sefirot ‘al Derekh She’elah u-Teshuvah, p. 5.

Jewish Mysticism
[E]ven though there is no boundary above… there is a boundary for everything that is grasped through the meditation of the heart (hirhur ha-lev) and the allusion of thought (remez ha-mahshavah) which emanates below to be found in speech and seen in action. Everything that is bounded has a measurement and corporeality, for everything that is grasped in the meditation of the heart is called a body (guf), even the spirit. Therefore, the sefirot, the principle for everything that is bounded (kelal le-khol mugbal), are the root (shoresh). This boundary that is without boundary (ha-gevul ha-hu’ mibeli gevul) emanated; thus it says [of the sefirot in Sefer Yesirah 1-7] “their measure is ten which have no end.”

Translated by Elliot Wolfson in Through a Speculum that Shines- Vision and Imagination in Medieval Jewish Mysticism, Princeton- Princeton University Press, 1994.