Sayyiduna Abu Sa'id al-Khudri (may Allah be pleased with him) said that the Prophet (peace and blessings be upon him) observed i'tikaf in the mosque. He (peace and blessings be upon him) heard the Companions reciting aloud while he (peace and blessings be upon him) was in his tent, so he (peace and blessings be upon him) drew back the curtain and said: "Are you not each conversing intimately with your Lord? Do not harm one another, and do not raise your recitation over one another in the prayer."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4703