From al-Sadiq (AS): Ali (AS) used to like to free himself for worship on four nights of the year, and they are: the first night of Rajab, the night of mid-Sha'ban, the night of the Feast of Fast-Breaking, and the night of the Feast of Sacrifice. (Misbah al-Za'ir, vol. 1, p. 299)
Imam al-Sadiq (AS) said: Ali (AS) liked to be alone and devote himself to worship on four nights of the year: the first night of Rajab, the night of mid-Sha'ban, the night of the Feast of Fast-Breaking, and the night of the Feast of Sacrifice.
It is narrated from Kumayl ibn Ziyad that he saw the Commander of the Faithful (AS) praying on the night of mid-Sha'ban while in prostration: 'O God, I ask You by Your mercy which encompasses all things.' (Misbah al-Za'ir, vol. 1, p. 317)
Kumayl narrates that Ali (AS) used to recite the supplication known as the Supplication of Kumayl while in the state of prostration.