ClearAll;
Eq1 = x'[t] == s*(y[t] - x[t]);
Eq2 = y'[t] == r*x[t] - y[t] - x[t]*(x[t]*y[t]/b);
Manipulate[
StreamPlot[{s*(y - x),
r*x - y - x*(x*y/b)}, {x, -Sqrt[b*(r - 1)] - 1,
Sqrt[b*(r - 1)] + 1}, {y, -Sqrt[b*(r - 1)] - 1,
Sqrt[b*(r - 1)] + 1}, StreamColorFunction -> "Rainbow"],
Delimiter,
{{T, 50}, 0.1, 100},
{{r, 1}, 1, 35},
{{s, 10}, 0, 100},
{{b, 8/3}, 0, 100},
SaveDefinitions -> True]

Plot3D[x*y*(3/8) == 0, {x, -10, 10}, {y, -10, 10}]