Hinduism
On thirteenth day of death a feast is organized. It is believed to be organised for the peace of the departed soul.
Christianity
* There were thirteen participants at the Last Supper. Tradition states that Judas Iscariot, the disciple who betrayed Jesus, was the 13th to sit at the table.
* Thirteen was once associated with the Epiphany by Christians, as it is said the child Jesus received the Magi on his thirteenth day of life.
* There are 13 Apostles in Christianity; the 12 Disciples plus St Paul, formerly Saul of Tarsus. In addition to being the 13th Apostle, he is also known as "The Apostle" by the Church Fathers.
Sikhism
According to famous Sakhi (Evidence) or story of Guru Nanak Dev Ji, when he was an accountant at a town of Sultanpur Lodhi, he was distributing grocery to people and when he gave groceries to the 13th person he stopped there because in Gurmukhi and Hindi the word 13 is called Terah, which means yours. And Guru Nanak kept on saying, "Yours, yours, yours..." remembering God. People reported to the emperor that Guru Nanak was giving out free food to the people. When treasures were checked, there was more money than before.
The word "Waheguru" appears only 13 times in Guru Granth Sahib, the Sikh holy scriptures and the eternal Guru.
The Vaisakhi which commemorates the creation of "Khalsa" or pure Sikh was celebrated on April 13 for many years.
Ik Onkar also looks like 13.