Is one who intentionally misses the eclipse prayer (salat al-kusuf and khusuf) sinful, and is he considered weak in faith?

The eclipse prayer (Salat al-Kusuf and Salat al-Khusuf) is a Sunnah, and there is no sin upon one who omits it. However, abandoning these Sunnah prayers indicates a lack of desire for reward and for an increase in faith, as every act of obedience increases faith and strengthens the heart.