Where does this shloka appear?

Question

Where does this shloka appear?

"Astadasa Puranesu Vyasena Vachanam Dwayam, Paropakaraya Punyaya – Papaya Para Peedanam"

Answer 1

This appears to a subhāṣita (wise saying), listed as No. 3587 in the Mahā-Subhāṣita-Saṅgraha. This collection in turn references other subhāṣita collections as its source so it probably doesn't belong to any Hindu scripture.

3587

अष्टादशपुराणेषु व्यासस्य वचनद्वयम् ।
परोपकारः पुण्याय पापाय परपीडनम् ॥

aṣṭādaśapurāṇeṣu vyāsasya vacanadvayam |
paropakāraḥ puṇyāya pāpāya parapīḍanam ||

[Secondary Sources:]

Subhāṣita-saptaśati 697, Saṃskṛta-sūktiratnākara 970, Subhāṣita-padya-ratnākara 753. 12 (a. Bhāgavata).

[Meaning:]

In the course of the eighteen Purāṇas, the sage Vyāsa has made two (very fine) statements: doing help to others results in religious merit, doing injury to others brings about sin. (A. A. R.).