Vijnana Bhairava Tantra
न चित्तं निक्षिपेद् दुःखे न सुखे वा परिक्षिपेत् । भैरवि ज्ञायतां मध्ये किं तत्त्वमवशिष्यते ॥ १०३ ॥
O Goddess, the mind should not dwell on pain or pleasure, but the essence that remains in the middle (in between the opposites) should be known.
english translation