"God does not fit in an occupied heart."

     St. John of the Cross, Llama de amor viva (The living flame of love) iii.48, trans. Kavanaugh & Rodriguez (Collected works of St. John of the Cross (Washington, DC:  ICS Publications, 1973), 628).

It [(the intellect)] thereby empties itself of everything comprehensible to it, because none of that is God; as we have said, God does not fit in an occupied heart.

Obras de San Juan de la Cruz, Doctor de la Iglesia, ed. Silverio de Santa Teresa, tom. 4 (Burgos:  Tipografia «El Monte Carmelo», 1931), 182:

pues que se va vaciando de todo lo que en él podia caer, porque nada de ello era Dios, pues, como habemos dicho, Dios no puede caber en él [(alternatively, from Madrid. Bib. Nac. Ms. 17.950, the variant translated by Kavanaugh & Rodriguez:  no puede caber en el corazón ocupado)]. . . .

Despite the phrase "as we have said" ("como habemos dicho"), an Adobe Acrobat search of the PDF of tom. 4 of the Obras (above) revealed no other occurrence of the exact phrase "no puede caber" in the Llama de amor viva (but two irrelevant occurrences on p. 365 of tom. 1 and p. 373 of tom. 3).