The longest individual innings in Test cricket, measured by time spent at the crease, was played by Hanif Mohammad of Pakistan. In a match against the West Indies at Bridgetown in January 1958, Hanif batted for 970 minutes (16 hours and 10 minutes), scoring 337 runs. This monumental effort was instrumental in Pakistan saving the Test match after following on.
When considering the number of balls faced, the record belongs to Gary Kirsten of South Africa. He faced 642 balls during his innings of 275 runs against England at Durban in December 1999, spending 878 minutes (14 hours and 38 minutes) at the crease.
These records highlight exceptional endurance and concentration, showcasing the players' ability to anchor their team's innings under challenging circumstances.