John Calvin in his Institutes of the Christian Religion (mid 16th Century) in Book 3, Chapter 1, section 1 mentions 1 John 5:7-8 without any doubt.
“In
addition to the aforementioned favorable evidence, the Comma can be
traced back through the Waldensian Church to the translation of the
Old Italic in the 2nd century. Moreover, in the 7th century,
at least 12 Old Latin mss contain the passage; at least 21 in the
8th century, and at least 189 in the 9th century. Over 6,000
Old Latin manuscripts remained unexamined to this day.”