A person may testify to a matter only if there is sufficient evidence to show that the person has personal knowledge of the matter.

United States v. Ruiz, 249 F.3d 643, 646-647 (7th Cir. 2001) (upholding trial court's admission of police officer's testimony about his partner's statements [concerning defendant's appearance and clothing, his conduct on....Federal Rule of Evidence 803(1) and comparable State rules create a hearsay exception for a statement setting forth the declarant's perception of an event or condition at the time the declarant makes the statement or immediately thereafter.

United States v. Tedder, 403 F.3d 836, 839 (7th Cir. 2005) (conviction of an attorney for conspiring to defraud the US by assisting a wagering enterprise, plus money laundering related to his participation in an offshore gambling scheme;defendant argued that the judge should have allowed him to present...Reputation or opinion is admissible to impeach a witness by showing the untruthfulness of the witness.

Leonard v. Nationwide Mut. Ins. Co., 499 F.3d 419, 442 (5th Cir. 2007) (holding that the district court erroneously admitted statements made by insurer's agent to policyholders as "habit" evidence under Federal Rule of Evidence 406 because "evidence was lacking to suggest that [insurer agent's] statements...The routine practice of an organization is admissible under Federal Rule of Evidence 406 or a comparable State rule in order to show the conduct of the organization on a particular occasion, but a volitional routine practice cannot be used to show the conduct of a specific person on a particular occasion.