I personally trust the Nestle-Aland/UBS (NU) manuscripts a bit more than the Textus Receptus (TR), as the TR is based on only a handful of late Greek manuscripts. The NU is based on a diverse collection of both early and late texts, and when discrepancies are found, the NU tends to defer to the earlier texts while still allowing the Majority Text to hold some level of sway in the translation.
The TR includes the line in question, while the NU does not.
You see Jesus' teaching on this matter in his interaction with the rich man in Matthew 19:18-19, Mark 10:19, and Luke 18:20, and in all of these cases, "do not bear false witness" is included.
When Paul summarizes this short list of a handful of the 10 commandments (Exodus 20:13-17, Deuteronomy 5:17-21) by quoting Jesus (Matthew 22:39, Mark 12:31, Luke 10:7) as saying "Love your neighbor as yourself," it becomes apparent that regardless of which source text is accurate in this instance, the intended message is unaffected. In fact, Jesus was possibly, or probably, quoting Leviticus 19:18, which also commands the Israelites to love their neighbors as themselves.
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