I was in a Dharma class last week when someone commented that Mahayana/Vajrayana Buddhists use the syllable 'Om' in dharanis/mantras like the Hindus.
Then I recalled some kalpas back when E-Sangha was up, there was a thread in the Mahayana Forum where someone raised the same issue and some user appended one link that has a purported Sutra where the Buddha reportedly taught on the syllable 'OM'. I regretted not saving that link.
Does anyone here recall or know of that link?
Many thanks in advance