Is it necessary to fast the White Days after fasting them the first time?

Fasting the White Days is supererogatory, not obligatory. Consistency in performing good deeds is better than doing them sometimes and abandoning them at other times, as the Messenger of Allah, peace and blessings be upon him, said: "And the most beloved of deeds to Allah are those that are most consistent, even if they are few." There is no validity to the claim that it is impermissible for someone who does not fast them consistently to observe them. Rather, it is recommended to fast them and to be consistent in doing so as much as possible. There is no harm in not fasting them, whether due to an excuse or otherwise.