[Snapshot14w25a]clickEvent

[Book]
/give @p minecraft:written_book 1 0 {pages:["{text:\"\",extra:[{text:\"Say\",clickEvent:{action:run_command,value:\"/say 123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890 \"}}]}"]}

[/tellraw]
/tellraw @p {text:"",extra:[{text:"Say",clickEvent:{action:run_command,value:"/say 123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890"}}]}

[Sign]
/setblock ~0 ~1 ~0 minecraft:standing_sign 0 replace {Text2:"{text:\"\",clickEvent:{action:run_command,value:\"/say 123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890 \"},extra:[{text:\"Say\"}]}"}