Reference for Bava Batra 118:1

ויכול למחות פחות מטפח אין לו חזקה ואין יכול למחות:

AND THE OWNER OF THE COURTYARD CAN PREVENT IT BEING MADE [IN THE FIRST INSTANCE]. IF IT IS LESS THAN A HANDBREADTH THERE IS NO <i>HAZAKAH</i> FOR IT AND HE CANNOT PREVENT IT [FROM BEING MADE].

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