The Cardiff-born star went 24 Premier League games without winning a game for Tottenham but soon moved from left-back to left-wing as his fortunes turned at White Hart Lane.
Bale's revival coincided with Tottenham's as they secured a top-four finish last term and Champions League football for this season.
And Bale scored in Tottenham's 4-1 Champions League victory over FC Twente on Tuesday, adding to his growing reputation as one of Europe's most feared wingers.
His form has led Redknapp to slap a 'not for sale' sign on Bale's head, with the Spurs boss determined to keep hold of one of his star assets.
"No-one's rung me about Gareth Bale, but we won't be selling Gareth," Redknapp told BBC Sport.
"We are building something at Tottenham, we want to establish ourselves and be right up there every season challenging for Champions League football and trophies.
Redknapp added: "He needs to stay with Tottenham and develop.
"He's gone from a lad who couldn't get in the team and then when he could, through no fault of his own, he had a horrendous record of not winning in the Premier League for 24 games, which played on his mind and played on my mind and everyone associated with the club."
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