I don't know which one said it, but they even explicitly point out that it is better for the number of reactionary representatives in parliament to increase than for the working class candidates to deradicalise their program, or sell out to the bourgeoise.

Marx:

“Even where there is no prospect of achieving their election the workers must put up their own candidates to preserve their independence, to gauge their own strength and to bring their revolutionary position and party standpoint to public attention. They must not be led astray by the empty phrases of the democrats, who will maintain that the workers’ candidates will split the democratic party and offer the forces of reaction the chance of victory. All such talk means, in the final analysis, that the proletariat is to be swindled. The progress which the proletarian party will make by operating independently in this way is infinitely more important than the disadvantages resulting from the presence of a few reactionaries in the representative body.”