Talmud (Rodkinson)/Seder Moed/Tractate Shabbat 2 a

Mishna 1

There are two acts constituting transfer¹ of movable things (over the dividing line of adjoining premises, based on biblical statutes). The two acts are, however, increased to four on the inside and to a like amount on the outside of the premises (by the addition of rabbinical statutes). How so? A mendicant stands outside and the master of a house inside. The mendicant passes his hand into the house (through a window or door) and puts something into the hand of the master, or he takes something out of the master's hand and draws it back (toward him). In such a case the mendicant is guilty (of transfer) and the master of the house is free. If the master of the house passes his hand outside and puts a thing into the hand of the mendicant, or takes something out of the mendicant's hand and brings it into the house, the master of the house is culpable and the mendicant is free.² If the mendicant extends his hand into the house and the master takes something out of it, or puts something into it which is drawn to the outside by the mendicant, they are both free. If the master of the house extends his hand outside and the mendicant takes something out of it, or puts something into it which is drawn to the inside by the master, they are both free.

Gemara

We were taught (Shebuoth, IV. 2): "The acts of transfer on the Sabbath are two, respectively four."