Shiva Purana
द्विखंडं स्थावरं लिंगं कर्तव्यं हि विधानतः । अखंडं जंगमं प्रोक्तंश् ऐवसिद्धान्तवेदिभिः ३२ ।
This has been mentioned by those who know the principles of Śaiva cult that a stationary phallic image shall be made of two pieces.
english translation
dvikhaMDaM sthAvaraM liMgaM kartavyaM hi vidhAnataH । akhaMDaM jaMgamaM proktaMz aivasiddhAntavedibhiH 32 ।
hk transliteration by Sanscript