Beggars can't be choosers
If you request something to be given you should not question what you are given.
This proverbial phrase has much in common with 'don't look a gift horse in the mouth' both in meaning and by virtue of having been first recorded in print by John Heywood. Both phrases were coined well before any form of organised state support for the poor and express the widely held mediaeval opinion that if you asked for and received a gift you should be grateful for it. The 'gift horse' proverb was recorded first, in Heywood's 1546 version of A dialogue conteinyng the nomber in effect of all the prouerbes in the Englishe tongue.
'Beggars should not be choosers' didn't appear until the 1562 version of 'Proverbs'.
Beggers should be no choosers, but yet they will:
Who can bryng a begger from choyse to begge still?
The proverb is more commonly expressed these days as 'beggars can't be choosers'. This leads to an ambiguity in meaning between 'beggars are unable to be choosers' and 'beggars ought not to be choosers'. Of course, the latter is the original meaning.
See also: the List of Proverbs.