Rasarnava 3.3

3.3

catvāraḥ pradhānagṛhāḥ haṃsagṛhaṃ tu pañcamam
yatra siddhir makārādiḥ tiṣṭhate pañcame gṛhe //

There are four primary chambers, and the fifth is the Haṃsa chamber,
where success beginning with the syllable "ma" abides in the fifth chamber.