In How Many Circumstances Can Prayer Remain? St. Isaac the Syrian
When the Spirit takes its dwelling place in a man he does not cease to pray, because the Spirit will constantly pray in him. Then, neither when he sleeps nor when he is awake, will prayer be cut off from his soul, but when he eats and when he drinks, when he lies down or when he does any work, even when he is immersed in sleep the perfumes of prayer will breathe in his heart spontaneously.
St. Isaac the Syrian.
