This incident happened during the 1971 tour of India to the west Indies. The tour was significant in many ways. It heralded the arrival of India's spinners as genuine match-winners.
In the 5th test at Port-of Spain. West Indies after getting India out for 360 were going strong , at 517-6. Maurice Foster was batting confidently and reached 99, David Holford and he had already added a handy 93 between them Sunil Gavaskar who was fielding at fine leg was asked by a spectator if he thought Maurice would get to his 100. Gavaskar said he would. The spectator felt he wouldn't and was willing to bet on it. They agreed that if Foster got out on 99, Gavaskar would pay him a pound and if Foster got to his 100, the spectator would give him 100 pounds.
Suddenly Foster became jittery. Three balls later, he edged one on to his stumps ! Out for 99. During tea break , Gavaskar took his pound on the field but couldn't find that spectator .. and with Foster's dismissal West Indies collapsed to 526 all out.