Question: Who did McCartney ask to contribute to the recording?
About the article "Let It Be", section "Concept".

Candidate passages:
The video accompanying the single was directed by Julien Temple and had to be re-edited as a brief glimpse of a woman skinnydipping caused a minor controversy.
Also appearing in the video were Ringo Starr, Linda McCartney (her final appearance in a music video) and the band Spud (although they are shown performing with McCartney, they did not contribute to the recording of the track).
The video debuted during an appearance on "The Oprah Winfrey Show". 
Written in early 1962, "Ask Me Why" is principally a John Lennon composition, but was credited to Paul McCartney and John Lennon, as were all other Lennon–McCartney originals on the first pressings of "Please Please Me" album.
Paul McCartney: "It was John's original idea and we both sat down and wrote it together, just did a job on it.
It was mostly John's."
(Barry Miles.
Paul McCartney: Many Years From Now).
It was part of their live act prior to their recording contract, and was one of the songs performed at their Parlophone audition in EMI's Abbey Road studio three on 6 June 1962.
The song emulates in style that of Smokey Robinson and the Miracles, by whom Lennon was influenced, and draws its opening guitar phrase from the Miracles’ "What’s So Good About Goodbye" (1961). 
McCartney recorded it on 9 August 1968.
He recorded 25 takes singing and playing acoustic guitar simultaneously.
Take 24 was perceived to be the best (take 2 later appeared on Anthology 3).
McCartney recorded overdubs of timpani, another guitar, and drums on 20 August when George Martin's orchestral contributions were also added.
The drums sound more like bongos and this was achieved by putting the drums halfway down an uncarpeted corridor with the mics at a far end which resulted in a staccato sound.
Lennon did not play on the recording, but McCartney said he contributed some words to the song in India.
When Lennon — who hated it whenever McCartney recorded without the rest of the band — walked into the studio with Ringo Starr after McCartney had finished, "you could have cut the atmosphere with a knife," recalled engineer Ken Scott. 
Other popular music.1970s.
As The Beatles were breaking up in 1970, McCartney was working on his debut solo album, "McCartney", which was released in April.
Backing vocals were provided by his wife, Linda, whom he had married the previous year.
McCartney had insisted from the beginning of their marriage that his wife should be involved in his musical projects, so that they did not have to be apart when he was on tour.
In May 1971 a second album, "Ram", credited to Paul and Linda McCartney and selling several million copies, was released, spawning the #1 U.S. hit single "Uncle Albert/Admiral Halsey".
The album was recorded with the help of outside musicians, including drummer Denny Seiwell, who had to perform in a secret audition for Paul and Linda before being chosen.
A jam session — with Lennon and McCartney — was recorded in California, in 1974, and released on the bootleg "A Toot and a Snore in '74".
In 1977, McCartney supervised the release of "Thrillington", an instrumental interpretation of "Ram", under the name "Percy 'Thrills' Thrillington".
At Christmas 1979, McCartney released a solo Christmas single, "Wonderful Christmastime", his first solo release since he began recording with Wings in 1971.
At the end of the 1970s Paul McCartney had become the 5th biggest selling music act on the planet. 
The company is most famous through its association with Beatles singer and instrumentalist Paul McCartney, who is a longtime user of the Höfner 500/1 model hollow-body electric bass, first manufactured in 1956.
McCartney played two left-handed 500/1 basses during most of the group's career – a 1961 model with pickups mounted close together towards the neck, and a 1962 model, with the second pickup mounted closer to the bridge.
McCartney used the 1961 bass until the recording of "With The Beatles" in late 1963, when he obtained his second 500/1.
McCartney used his 1962 bass almost exclusively during The Beatles' touring career, using his 1961 bass (which was repaired and refinished in 1964) as a backup.
Although by 1965 McCartney had begun using a Rickenbacker bass in-studio, he did bring out his 1961 model for the "Revolution" promo film in 1968 and for the documentary "Let It Be" the following year.
During the shooting, however, the 1961 bass was stolen, and McCartney used his newer Höfner for the remainder of the film, including the famous rooftop performance.
McCartney has continued to use his 1963 Höfner extensively throughout his solo career and continues to use it today.