Is my oath regarding my sister's absolute salary and my owning sheep, even though I haven't seen them, considered a 'yamin ghamus' (a perjurious oath)?

The fundamental principle of giving testimony is that it must be based on direct observation and knowledge, as Allah the Almighty says: "But only he who testifies to the truth and he knows." Swearing falsely is one of the gravest sins. If the testimony is based on a known truth established by direct observation or certain hearing, then there is no objection. However, if it is false, a mere rumor, or news that does not reach the level of certainty, then it is impermissible. Swearing an oath upon it is a grave error that necessitates sincere repentance and compensation for any consequences that result from it.