Vijnana Bhairava Tantra
देहान्तरे त्वग्विभागम् भित्तिभूतम् विचिन्तयेत् । न किंचिदन्तरे तस्य ध्यायन्नध्येयभाग्भवेत् ॥ ४८ ॥
One should contemplate on the skin of the body as a mere wall or partition with nothing inside it. By meditating thus, he becomes like the void, which cannot be meditated upon.
english translation
dehAntare tvagvibhAgam bhittibhUtam vicintayet । na kiMcidantare tasya dhyAyannadhyeyabhAgbhavet ॥ 48 ॥
hk transliteration by Sanscript