In line 3, the “sending State” is the one capable of expelling foreign diplomats from its territory.

Withdrawal of a Diplomatic Mission

1 The recall of an entire diplomatic mission, whether
on a temporary or on an indefinite basis, without breach of
diplomatic relations between sending and receiving States,
4 is now a relatively frequent procedure. Recall may take
place for political, economic or security reasons. In all cases
the two States remain formally in diplomatic relations and
7 there are no constraints in their contacts at international
conferences or organisations or in third States. Normally, it
is hoped that a permanent diplomatic mission may be re-
10 established under more favourable circumstances, and this is
more straightforward when no formal breach of relations has
taken place. Formal breach is usually very difficult to
13 reverse quickly, even if the reason for it has disappeared. In
1956, for example, Saudi Arabia broke relations with the
United Kingdom and France on 6 November, one day before
16 the cease-fire which brought an end to their intervention in
Suez, but relations were not restored between Saudi Arabia
18 and either State until 1962.

I. Roberts (org.). Satow’s Diplomatic Practice. Oxford: Oxford University Press, 2009, p. 215, with adaptations.