Sayyiduna Abu Hurayrah (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings be upon him) said: "When any of you stands for prayer at night and the Qur'an does not come out properly on his tongue, so that he does not know what he is saying, let him lie down."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4730