Shiva Purana
इदं परमिदं नेति विवादस्सुमहानभूत् ॥ परस्य दुर्निरूपत्वान्न जातस्तत्र निश्चयः ॥ ३ ॥
There was a great debate as to whether this was the highest or not. Because the other is poorly defined there is no certainty about it.
english translation
idaM paramidaM neti vivAdassumahAnabhUt ॥ parasya durnirUpatvAnna jAtastatra nizcayaH ॥ 3 ॥
hk transliteration by Sanscript