Fiqh-us-Sunnah Volume 2, Supererogatory Prayer, Fiqh 2.036.
Section : The time for al-kasuf is from the beginning of the eclipse until the eclipse finishes.
The prayer of the lunar eclipse is similar to that of the solar eclipse. Al-Hassan al-Basri reports: “There was a solar eclipse and Ibn ‘Abbas, the governor of Basra, went out and prayed two rak’at with two ruku’ in each rak’ah. Then, he mounted his mount and said: ‘I prayed as I have seen the Prophet praying.'” This is related by ash-Shaf’i in his Musnad.