Contradiction with John 14:13
In this verse, Jesus says to ask in His name and He will do it, which implies direct intervention by Jesus, whereas John 16:26 implies asking through Him, but not necessarily by Him.
John 14:13: And whatsoever ye shall ask in my name, that will I do, that the Father may be glorified in the Son.
Contradiction with John 15:16
Here, Jesus emphasizes asking the Father in His name to receive what is asked, suggesting a direct response, which contrasts with the intermediary role suggested in John 16:26.
John 15:16: Ye have not chosen me, but I have chosen you, and ordained you, that ye should go and bring forth fruit, and [that] your fruit should remain: that whatsoever ye shall ask of the Father in my name, he may give it you.
Contradiction with John 16:23
This states that the Father will give whatever is asked in Jesus' name, suggesting immediate granting of requests, whereas John 16:26 implies a more mediated approach.
John 16:23: And in that day ye shall ask me nothing. Verily, verily, I say unto you, Whatsoever ye shall ask the Father in my name, he will give [it] you.
Contradiction with 1 John 5:14
This verse suggests the necessity of asking according to God's will, which adds a condition not explicitly mentioned in John 16:26.
1 John 5:14: And this is the confidence that we have in him, that, if we ask any thing according to his will, he heareth us: [in: or, concerning]