\[ y'(x)-f(a x+b y(x))=0 \] ✓ Mathematica : cpu = 10.9949 (sec), leaf count = 108
\[\text {Solve}\left [c_1=\int _1^{y(x)} \left (-\int _1^x \frac {a b^2 f'(a K[1]+b K[2])}{(b f(a K[1]+b K[2])+a)^2} \, dK[1]-\frac {b}{b f(b K[2]+a x)+a}\right ) \, dK[2]+\int _1^x \frac {b f(a K[1]+b y(x))}{b f(a K[1]+b y(x))+a} \, dK[1],y(x)\right ]\]
✓ Maple : cpu = 0.138 (sec), leaf count = 37
\[ \left \{ y \left ( x \right ) ={\frac {{\it RootOf} \left ( \int ^{{\it \_Z}}\! \left ( f \left ( {\it \_a}\,b \right ) b+a \right ) ^{-1}{d{\it \_a}}b-x+{\it \_C1} \right ) b-ax}{b}} \right \} \]