Step 1: Understanding the question.
We need to find which of the four options is NOT a principle of F.W. Taylor's Scientific Management but belongs to someone else's theory.
Step 2: Recall Taylor's core principles.
F.W. Taylor proposed four main principles: (1) Science, not rule of thumb, (2) Harmony, not discord, (3) Cooperation, not individualism, and (4) Maximum output instead of restricted output, along with the development of each worker to their greatest efficiency.
Step 3: Check option (A) - "Science, not rule of thumb."
This is Taylor's first and most fundamental principle, which insists on using scientific study and method instead of old-fashioned guesswork. It is genuinely a Taylor principle.
Step 4: Check option (C) - "Harmony, not discord."
This is also one of Taylor's principles, advocating a cooperative, mutually respectful relationship between management and workers instead of conflict. It is genuinely a Taylor principle.
Step 5: Check option (D) - "Maximum output instead of restricted output."
Taylor believed in maximizing production through scientific methods and incentives, explicitly opposing the workers' informal practice of deliberately slowing production. This too is a Taylor principle.
Step 6: Check option (B) - "Stability of Tenure."
Stability of Tenure of Personnel is Principle 13 of Henri Fayol's 14 General Principles of Management. It states that employees should not be changed too frequently and should be given time to settle into their roles. It has nothing to do with Taylor's shop-floor scientific management theory.
\[ \boxed{ \text{Stability of Tenure belongs to Fayol, NOT Taylor} } \]