Conversation so far:
What is Stax?
Stax Records is an American record label, originally based in Memphis, Tennessee.
What did Sam & Dave make at Stax Records?
Hold On, I'm Comin', released in March 1966, was an enormous R&B hit for Sam & Dave, and also their first single to break into the Top 40 Pop charts.
What singles were produced at Stax Records by Sam & Dave?
Recorded primarily at Stax Records in Memphis, Tennessee, from 1965 through 1968, these included Soul Man, Hold On, I'm Comin', and many other Southern Soul classics.

Question: What was their most popular song?
Self-contained rewrite: What was Sam & Dave's most popular song?