Assalaamu alaykum. There is a hadith about ‘Umar's, may Allaah be pleased with him, finger touching ‘Aa’ishah, may Allaah be pleased with her, by mistake, is this authentic?

All perfect praise be to Allaah, The Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad is His slave and Messenger. 

This hadeeth was reported by An-Nasaa’i in As-Sunan Al-Kubra from Mujaahid from ‘Aa’ishah who said, “I was eating Hays (kind of food) with the Messenger of Allaah in a dish. ‘Umar passed by, so he (the Messenger of Allaah) invited him in and he ate with us. My finger touched his, so ‘Umar said, 'Oh! If I were obeyed regarding you (Prophets' wives), then no eye would see you.' So the verse about the hijab was revealed.”

Some scholars classified this hadeeth as strong, such as As-Suyooti in Ad-Durr Al-Manthoor, as he said about it, “Its chain of narrators is saheeh (sound).”

Al-Albaani said in As-Silsilah As-Saheehah, “Its chain of narrators is good.”

However, Ad-Daaraqutni, classified it as weak in Al-‘Ilal and said that it is a Mursal hadeeth (i.e. a report narrated on the authority of some of the Taabi'oon [the generation that followed the Companions]), from Mujaahid. The Mursal hadeeth is one of the categories of the weak hadeeth.

In any case, even if we presume that this hadeeth is authentic, it does not constitute any contradiction, because the incident happened before the revelation of the verse about the hijab and before the hijab was imposed on Muslim women.

Allaah knows best.