No evidence of bits of grain in grass (7)
I believe the answer is:
hearsay
'no evidence' is the definition.
(hearsay about something is not reliable evidence)
'bits of grain in grass' is the wordplay.
'bits of grain' becomes 'ears' (ear can mean a piece of corn).
'in' indicates putting letters inside.
'grass' becomes 'hay' (hay is dried grass).
'ears' inserted within 'hay' is 'HEARSAY'.
'of' is the link.
(Other definitions for hearsay that I've seen before include "Gossip passed around by word of mouth" , "Common talk" , "speculation" , "Gossip or rumour - not allowed as evidence" , "Gossip or idle talk - it's not evidence" .)