The phrase "knowing him for" is correct and it can be used in written English.
You can use this phrase when you are speaking about the length of time you have known someone. For example, "I have been knowing him for 8 years now."
"I can't explain it, knowing him for nearly twenty years, I feel so privileged," Carol said.
"My backing of Zac is purely [based] on knowing him for 22 years and urging him to go into politics".
We had the good fortune of knowing him for 35 years and of being introduced to the "Old Sod" by Tom.
After knowing him for a while, I wondered if the discontent and suppressed anger that sometimes showed on his face were the result of having to do an extra job, one unequal to his talents.
It pressed the moral outrage button with the struggle of its young heroine, Sally Middleton, to cope with her sexual desires, her confession to her ardent paramour that "there is a beast in me, too" and her decision to sleep with him after knowing him for only a weekend.
Shortly beforehand Shaun Wright-Phillips had come on to cheers from City's fans, remembering the player of old, and abuse from the away end, knowing him for what he is now: a symbol of the club's excesses, making a fortune out of almost nothing.
I saw Maysles — or, rather, Al, since I had the privilege of knowing him casually — for the last time in September, at a memorial celebration of Robert Drew, the producer who, with "Primary," in 1960, revolutionized American documentary filmmaking.
The good news for United fans is that probably means a rare start for Dimitar Berbatov; knowing him — he tied for the Premier League lead with 20 goals last year despite losing his job — he'll probably get a hat trick.
Mr. Lang said he wanted a "playful dessert" that would reflect Mr. Maazel's personality, "because underneath this incredible conducting control that Lorin has, Jennifer and I feel, knowing him so well for so long, there is a playfulness".
He will be sorely missed by all those whose lives he touched, and I know we are all the richer for knowing him.
But we are better for knowing him.
