Is refraining from seeking forgiveness (Istighfar) due to remembering specific sins considered a whisper from Satan (waswasa), or is repentance from all sins a prerequisite for seeking forgiveness?

Seeking forgiveness (Istighfar) is one of the greatest acts of drawing closer to Allah, a cause for blessings, and a shield against evils. It is a request for Allah's forgiveness. Istighfar is valid from both the repentant and the non-repentant, but its perfection is attained when accompanied by sincere repentance, remorse for the sin, and a firm resolve not to repeat it. It is a virtuous act that should not be abandoned. Satan may try to discourage one from seeking forgiveness. Istighfar is sought after and praised in the Qur'an, and Allah forgives those who seek His forgiveness. Mere Istighfar is a request for forgiveness and a supplication (dua), and its ruling is the same as any other supplication. Allah may answer the one who makes it, especially if it emanates from a broken heart or coincides with times when supplications are answered. As for Istighfar of the tongue while the heart insists on the sin, it is merely a supplication, and Allah knows best whether He answers it or rejects it.