Sahih Bukhari Volume 003, Book 048, Hadith Number 806.
Narated By Abdullah bin Umar : Allah's Apostle and Ubai bin Kab Al-Ansari went to the garden where Ibn Saiyad used to live. When Allah's Apostle entered (the garden), he (i.e. Allah's Apostle) started hiding himself behind the datepalms as he wanted to hear secretly the talk of Ibn Saiyad before the latter saw him. Ibn Saiyad wrapped with a soft decorated sheet was lying on his bed murmuring. Ibn Saiyad's mother saw the Prophet hiding behind the stems of the date-palms. She addressed Ibn Saiyad saying, "O Saf, this is Muhammad." Hearing that Ibn Saiyad stopped murmuring (or got cautious), the Prophet said, "If she had left him undisturbed, he would have revealed his reality." (See Hadith No. 290, Vol 4 for details)