Katha Upanishad - Verse 1.3.17
Text: य इमं परमं गुह्यं श्रावयेद्ब्रह्मसंसदि । प्रयतः श्राद्धकाले वा तदानन्त्याय कल्पते तदानन्त्याय कल्पत इति ॥ १७ ॥ ya imaṃ paramaṃ guhyaṃ śrāvayedbrahmasaṃsadi | prayataḥ śrāddhakāle vā tadānantyāya kalpate tadānantyāya kalpata iti || 17 || 17. Whoever with zeal, causes to be recited before an. assembly of Brahmins or at the time of Sraddha of the ancestors, this highest secret, that secures immortality, secures immortality. Shankara’s Commentary: Whoever causes this text, this highest secret to be recited verbatim and with meaning, in an assembly of Brahmins, being himself clean, or causes it to be recited at the time of Sraddha to those who are there fed, that Sraddha is able to secure for him endless fruits....